- Cartography, History of Cartography, Nautical cartography and navigational science in the Mediterranean World from the Late Middle Ages to the 18th century, History of Navigation, Modeling and Simulation, Navigation, and 6 morePortolan charts, Mathematical Cartography, Historical Geography, Geographic Information Systems (GIS), Medieval Cartography, and Fernao de Magalhaesedit
- I am a retired Navy Captain, and a specialist in Navigation, Hydrographic Surveying and Mathematical Cartography, now... moreI am a retired Navy Captain, and a specialist in Navigation, Hydrographic Surveying and Mathematical Cartography, now a researcher at the Centre for the History of Science and Technology, University of Lisbon. From about 2006 onward I have been doing research on the geometry, construction and use of pre-Mercator nautical charts. Since June 2017, I have been leading the European Research Council project MEDEA-CHART, dedicated to the study of medieval and early modern nautical charts.edit
"Juan de la cosa la fizo en el puerto de S: mã en año de 1500" (Juan de la Cosa made it in the port of Santa Maria, in 1500) is the inscription written below the figure of Saint Christopher walking on the water, near the left margin of... more
"Juan de la cosa la fizo en el puerto de S: mã en año de 1500" (Juan de la Cosa made it in the port of Santa Maria, in 1500) is the inscription written below the figure of Saint Christopher walking on the water, near the left margin of the oldest extant nautical planisphere of the early modern period. One of the most striking features of the planisphere is the exaggerated size of the Caribbean Sea, whose scale appears much inflated relative to the one of Europe of Africa. This distortion, which was replicated in all subsequent nautical charts for more than twenty years, was caused by the faulty latitude measurements made by Columbus during his first two voyages to the Caribbean.
Chart of the Week series of mini articles published in the Medea-Chart project website
An old parchment is kept at the French National Library containing the earliest known nautical chart to have survived to the present day, the Carte Pisane (Pisan Chart). It represents the Mediterranean Sea and the western half of the... more
An old parchment is kept at the French National Library containing the earliest known nautical chart to have survived to the present day, the Carte Pisane (Pisan Chart). It represents the Mediterranean Sea and the western half of the Black Sea, as well as the northwest coast of Europe and the southern part of Britain. Rather than being the first of its kind, the Carte Pisane is believed to be the result of a long period of development that has left no known material evidence and may have extended to near the beginning of the 13th century, when the marine compass was already in use and the first prototypes based on compass directions were likely created.
In 1517 Fernão de Magalhães (Ferdinand Magellan) arrived at Seville, with an irresistible proposal to the young King Charles I of Spain: to demonstrate that the coveted Spice Islands(the Moluccas, source of the valuable clove) were on the... more
In 1517 Fernão de Magalhães (Ferdinand Magellan) arrived at Seville, with an irresistible proposal to the young King Charles I of Spain: to demonstrate that the coveted Spice Islands(the Moluccas, source of the valuable clove) were on the Spanish side of the world according to the Treaty of Tordesillas and could be reached by navigating to the west. The Kunstmann IV planisphere, offered by Magellan to the king and based on contemporary Portuguese cartography, was part of his argument.
The Cantino planisphere is one of the most precious monuments of the world’s cartographic heritage. It was drawn by an anonymous Portuguese cartographer, in 1502 and immediately taken to Italy by Alberto Cantino, an emissary of the Duke... more
The Cantino planisphere is one of the most precious monuments of the world’s cartographic heritage. It was drawn by an anonymous Portuguese cartographer, in 1502 and immediately taken to Italy by Alberto Cantino, an emissary of the Duke of Ferrara. It depicts the world as Europeans knew it in the wake of recent Spanish and Portuguese voyages of exploration to the Americas, Africa, and India. Together with the Kunstmann III anonymous chart of the Atlantic Ocean (c.1501-1506), it is one of the earliest nautical charts depicting the places according to observed latitudes.
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Nova et aucta orbis terrae descriptio ad usum navigantium emendate accomodata (‘New and augmented description of the Earth corrected for use in navigation’) is the title of the large, engraved world map that Gerardus Mercator presented to... more
Nova et aucta orbis terrae descriptio ad usum navigantium emendate accomodata (‘New and augmented description of the Earth corrected for use in navigation’) is the title of the large, engraved world map that Gerardus Mercator presented to the world in 1569. In this nautical planisphere, parallels and meridians form a regular mesh of rectangles where the spacing between adjacent parallels increase with latitude, in such a way as to make the projection conformal (that is, locally preserving all angles) and represent the lines of constant course as straight segments correctly oriented to the meridians. Only very recently was it possible to demonstrate, both numerically and historically, that the projection was most likely calculated using a ‘table of rhumbs’, that is, a table of geographical coordinates aimed at representing rhumb lines on a globe.
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A study of two Portuguese nautical charts of the sixteenth century, here designated as the ‘Atlas of Valladolid’, has been carried out with the aim of determining their origin and date of compilation. These charts are little known among... more
A study of two Portuguese nautical charts of the sixteenth century, here designated as the ‘Atlas of Valladolid’, has been carried out with the aim of determining their origin and date of compilation. These charts are little known among the international community and have never been subjected to a cartometric analysis. Based on stylistic considerations, on the comparison of the toponyms with other contemporary charts and on the analysis of the latitude errors, it is concluded that the two charts were likely to have been drawn by the Portuguese cartographer Gaspar Viegas before 1534.
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The earliest known historical clue to what might be a primitive nautical chart is in a medieval manuscript of c.1200, the Liber de existencia riveriarum et forma maris nostri mediterranei, which describes the Mediterranean Sea. The body... more
The earliest known historical clue to what might be a primitive nautical chart is in a medieval manuscript of c.1200, the Liber de existencia riveriarum et forma maris nostri mediterranei, which describes the Mediterranean Sea. The body of the manuscript consists of an account of the Mediterranean and Black seas and the Atlantic coasts of Europe and northern Africa organized in 45 regional sections, each introduced by a short text setting out the orientation and size of the region, followed by a portolan-like listing of contiguous coastal localities with the distances between them. These are complemented by additional tracks across the open sea (pelagic tracks) for which both distances and directions are provided. Two distinct types of directions can be distinguished: those not affected by magnetic declination, which indicates that they were probably determined by astronomical methods, and those affected by systematic errors that could only have originated in observations made with a marine compass. It is suggested that some of the pelagic courses in the Liber were compiled from an existing chart or sketch based on astronomical directions, which may have been used as a general reference for the work. The implication is that the genesis and technical evolution of the medieval portolan chart were more complex than has hitherto been thought by map historians, who have based their analyses on the few extant exemplars from the end of the thirteenth and beginning of the fourteenth centuries, all based on compass directions.
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During the sixteenth century and beyond, nautical charts were the single most important source of geographical information for the image of the world that was depicted in European maps and atlases. However, little was known until very... more
During the sixteenth century and beyond, nautical charts were the single most important source of geographical information for the image of the world that was depicted in European maps and atlases. However, little was known until very recently about the geometry of these remarkable artefacts. Making use of results obtained with modern techniques of cartometric analysis and numerical modeling, we clarify the nature of the early modern nautical chart and show how its geometry is intimately connected with the contemporaneous navigational methods. Two major conclusions follow from our study: firstly, nautical charts can only be understood in full cognizance of the navigational techniques they were intended to support; and secondly, nautical charts were instruments for navigation, not attempts at representing the Earth.
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A manuscript nautical chart in the Museu de Marinha (Navy Museum) in Lisbon, Portugal, contains the earliest known depiction of lines of constant magnetic declination (isogones). The unsigned and undated chart represents the Philippine... more
A manuscript nautical chart in the Museu de Marinha (Navy Museum) in Lisbon, Portugal, contains the earliest known depiction of lines of constant magnetic declination (isogones). The unsigned and undated chart represents the Philippine Sea and part of the Pacific Ocean. A series of curved lines graduated in points according to the value of the magnetic declination is arranged symmetrically in relation to the equator. Comparison of these lines with the spatial distribution of magnetic declination in the area in 1600, as given by the two modern geomagnetic models discussed below, suggests that this particular representation may reflect some observations made in situ, although with significant errors. Thus this chart predates by more than a century the printed isogonic chart of the Atlantic made by the English astronomer Edmond Halley in 1702, hitherto considered the earliest of its kind.
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The chart drawn by Juan de la Cosa in 1500 contains an important innovation that distinguishes this planisphere from the other nautical charts produced at the time: the depiction of the Equator and the Tropic of Cancer. This is a sign... more
The chart drawn by Juan de la Cosa in 1500 contains an important innovation that distinguishes this planisphere from the other nautical charts produced at the time: the depiction of the Equator and the Tropic of Cancer. This is a sign that astronomically observed latitudes may have been incorporated into the representation. In order to investigate such a possibility, the results of a cartometric analysis focused on the representation of the Atlantic and Indian Ocean coastlines are presented and discussed in this article, and several revealing conclusions will be drawn from the resulting analysis.
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An assessment of the navigational accuracy of the Mercator world map of 1569 is made, aimed at better understanding how the information was adapted from the contemporary cartography. At the time the map was engraved, navigational charts... more
An assessment of the navigational accuracy of the Mercator world map of 1569 is made, aimed at better understanding how the information was adapted from the contemporary cartography. At the time the map was engraved, navigational charts were constructed on the basis of astronomically-observed latitudes, magnetic courses and estimated distances between places. Before this information could be incorporated into the new world map it should be first transformed in such a way that the longitudinal spacings between places were restored to their correct values, as defined on the surface of the Earth. The question of whether Mercator performed such transformations or just considered that the positions were approximately correct has hitherto never been addressed in the literature. It is demonstrated in this article that Mercator was not fully aware of the complexity of the contemporary charts – which he considered to implicitly comprise a square grid of meridians and parallels – and that all planimetric information was directly imported to the novel world map without correction. It is further shown that the Mercator projection was not compatible with the navigational methods of the time
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In this paper, the results of a cartometric analysis of a number of Portuguese and Spanish charts of the sixteenth and seventeenth centuries are presented and conclusions are drawn concerning the length of the degree of latitude adopted... more
In this paper, the results of a cartometric analysis of a number of Portuguese and Spanish charts of the sixteenth and seventeenth centuries are presented and conclusions are drawn concerning the length of the degree of latitude adopted in the Iberian nautical cartography of the Renaissance. Under the light of what we know about the navigational and charting methods of the time, a new interpretation of the textual and cartographic sources is proposed. Rather than being the result of technical considerations or precise measurements, the adoption of the various standards during this long period appears to be no more than the echoes of the traditional models of the Earth and of the political disputes between Portugal and Spain
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The earliest extant cartographic representation of the Americas is on the 1500 planisphere by the Cantabrian pilot Juan de la Cosa. On this nautical chart, the New World is represented according to the information collected by Spanish,... more
The earliest extant cartographic representation of the Americas is on the 1500 planisphere by the Cantabrian pilot Juan de la Cosa. On this nautical chart, the New World is represented according to the information collected by Spanish, English and Portuguese explorers in the last years of the fifteenth century. One of its most striking features is the large size of the Antilles, which are represented with a remarkably exaggerated scale relative to Europe. This feature was later replicated in the Cantino (1502), the Caverio (c. 1504) and many other planispheres of the first quarter of the sixteenth century. In this article, the results of a cartometric analysis of a sample of nautical charts, from 1500 to 1525, are presented and discussed with the aim to better understand how the representation of the Caribbean Sea evolved over time. The analysis has shown that the earliest charts in which the mistake in proportion was fully corrected are the Castiglione and the Salviati planispheres of 1525, both produced by the Casa de Contratación of Seville. It is further concluded that the Spanish cartographic production of the Casa was the object of a considerable improvement, in quantity and quality, as a result of the Magellan-Elcano circumnavigation of 1519–22. This was made possible by the technical assistance of Portuguese cartographers and pilots during the preparation and execution of the voyage.
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This paper explains how, following the introduction of astronomical navigation, the transition between the portolan-type chart of the Mediterranean and the latitude chart of the Atlantic was facilitated by the small values of the magnetic... more
This paper explains how, following the introduction of astronomical navigation, the transition between the portolan-type chart of the Mediterranean and the latitude chart of the Atlantic was facilitated by the small values of the magnetic declination occuring in western Europe during the Renaissance. The results of two preliminary cartometric studies of a sample of charts of the sixteenth century are presented, focused on the latitude accuracy in the representation of northern Europe and the evolution of the longitudinal width of the Mediterranean and Africa.
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The results of a cartometric analysis of the early sixteenth-century Portuguese chart of the world known as the Cantino planisphere are presented and discussed. The focus is on errors affecting the geographic lines and the representation... more
The results of a cartometric analysis of the early sixteenth-century Portuguese chart of the world known as the Cantino planisphere are presented and discussed. The focus is on errors affecting the geographic lines and the representation of the coastlines. The outputs of three types of analyses are considered: a quantitative assessment of scales (scales of latitude and scales of distance); a qualitative evaluation of the implicit grid of meridians and parallels underlying the representation; and an assessment of the accuracy of latitudes. From these, details were obtained about the chart's construction, some contradicting previous interpretations, which allowed connections to be established between the depiction of certain areas on the chart and contemporary voyages of exploration. It is concluded that the geometry of the Cantino planisphere is fully explained by the use of the cartographic methods of the Renaissance once the effect of magnetic declination is taken into account.
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A numerical model using the concept of multidimensional scaling, generalized to distances and directions measured on the surface of the Earth, is presented and tested, with the objective of simulating the main geometric features of early... more
A numerical model using the concept of multidimensional scaling, generalized to distances and directions measured on the surface of the Earth, is presented and tested, with the objective of simulating the main geometric features of early nautical charts. Starting with a sample of points defined by their latitudes and longitudes, the process consists in rearranging their positions in a plane so that the differences between the initial (spherical) and final (planar) distances and directions between them are minimized. The geometry of the Cantino planisphere (1502) is simulated and the output is compared with the geographic grid implicit to the original chart, with satisfactory results. The model proved to be an effective and easy-to-use research tool and may be used, not only for simulating and assessing the various factors affecting the geometry of early nautical charts, but also for educational purposes e.g. illustrating the properties of map projections
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Abstract of PhD thesis with same name (published September 2010)
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For more than two centuries much has been written about the origin and method of construction of the Mediterranean portolan charts; still these matters continue to be the object of some controversy as no one explanation was able to... more
For more than two centuries much has been written about the origin and method of
construction of the Mediterranean portolan charts; still these matters continue to be the object
of some controversy as no one explanation was able to gather unanimous agreement among
researchers. If some theory seems to prevail, that is certainly the one asserting the medieval
origin of the portolan chart, which would have followed the introduction of the marine
compass in the Mediterranean, when the pilots start to plot the magnetic directions and
estimated distances between ports observed at sea. In the research here presented a numerical
model which simulates the construction of the old portolan charts is tested. This model was
developed in the light of the navigational methods available at the time, taking into account
the spatial distribution of the magnetic declination in the Mediterranean, as estimated by a
geomagnetic model based on paleomagnetic data. The results are then compared with two
extant charts using cartometric analysis techniques. It is concluded that this type of
methodology might contribute to a better understanding of the geometry and methods of
construction of the portolan charts. Also, the good agreement between the geometry of the
analysed charts and the model’s results clearly supports the a-priori assumptions on their
method of construction.
construction of the Mediterranean portolan charts; still these matters continue to be the object
of some controversy as no one explanation was able to gather unanimous agreement among
researchers. If some theory seems to prevail, that is certainly the one asserting the medieval
origin of the portolan chart, which would have followed the introduction of the marine
compass in the Mediterranean, when the pilots start to plot the magnetic directions and
estimated distances between ports observed at sea. In the research here presented a numerical
model which simulates the construction of the old portolan charts is tested. This model was
developed in the light of the navigational methods available at the time, taking into account
the spatial distribution of the magnetic declination in the Mediterranean, as estimated by a
geomagnetic model based on paleomagnetic data. The results are then compared with two
extant charts using cartometric analysis techniques. It is concluded that this type of
methodology might contribute to a better understanding of the geometry and methods of
construction of the portolan charts. Also, the good agreement between the geometry of the
analysed charts and the model’s results clearly supports the a-priori assumptions on their
method of construction.
Research Interests:
The first nautical charts used to navigate in the Atlantic, in the late Middle Ages and Renaissance, were identical to the portolan charts of the Mediterranean, only differing in their geographic limits. With the introduction of... more
The first nautical charts used to navigate in the Atlantic, in the late Middle Ages and
Renaissance, were identical to the portolan charts of the Mediterranean, only differing
in their geographic limits. With the introduction of astronomical navigation, and
when a scale of latitudes was for the first time added to these charts, it quickly became
obvious that their geometry had to be modified in accordance with the new
navigational methods. The resulting hybrid model represented a major breakthrough
in the nautical cartography of the Renaissance, marking the beginning of the evolution
form the “maps based on routes”, to the Ptolemy’s system of geographical coordinates.
Using cartometric analysis, and taking into account the navigational
methods used in the 16th century, it will be shown that these charts were projectionless,
in the sense that they were constructed plotting directly on the plane the observed
latitudes, courses and distances, as if the Earth were flat.
Renaissance, were identical to the portolan charts of the Mediterranean, only differing
in their geographic limits. With the introduction of astronomical navigation, and
when a scale of latitudes was for the first time added to these charts, it quickly became
obvious that their geometry had to be modified in accordance with the new
navigational methods. The resulting hybrid model represented a major breakthrough
in the nautical cartography of the Renaissance, marking the beginning of the evolution
form the “maps based on routes”, to the Ptolemy’s system of geographical coordinates.
Using cartometric analysis, and taking into account the navigational
methods used in the 16th century, it will be shown that these charts were projectionless,
in the sense that they were constructed plotting directly on the plane the observed
latitudes, courses and distances, as if the Earth were flat.
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The earliest known reference to a nautical chart is in a Latin manuscript of ca.1200, the Liber de existencia riveriarum et forma maris nostril mediterranei, written probably by a cleric in Pisa, with the explicit purpose of describing... more
The earliest known reference to a nautical chart is in a Latin manuscript of ca.1200, the Liber de existencia riveriarum et forma maris nostril mediterranei, written probably by a cleric in Pisa, with the explicit purpose of describing the Mediterranean Sea. In the prologue of the document, a reference is made to a chart that was constructed by the author and to how the information about the relative positions of the places in the Mediterranean was provided by the mariners and their rutters, as well as by the information the author could collect in his own voyages. Most part of the manuscript consists in a systematic listing of places and distances along the coast, organized in regional sections, each of them introduced by a short text indicating the orientation and size of the region. This information is complemented by a number of tracks connecting places situated in different regions, or between coastal places and islands (pelagic tracks), for which both distances and directions are provided. The analysis of these pelagic tracks suggests that most of the information was read from a chart while other may have been compiled from pilots’ rutters. An important point to note is that all directions are indicated in accordance to the eight classical winds, as in the oldest wind roses, to which eight intermediate ones were added.
In this paper I will show that many directions of the pelagic routes noted in the Liber could not have been measured with a marine compass because they are not affected by magnetic declination. This implies that they must have been determined using astronomical methods, for example, by taking the direction of the Pole Star or of the rising and setting of known stars as references. If most of the pelagic directions in the Liber were in fact taken from a chart, as indicated in the document, this means that a primitive type of portolan chart, not based on compass directions, was being developed at about 1200. This conclusion is consistent with the earliest extant references to the marine compass, which indicate that its use on board was exceptional during the last decades of the twelfth century.
It is further concluded that the genesis and technical evolution of the medieval portolan chart is a much longer and complex process than previously considered by the historians, who have based their analyses on the very few extant exemplars of the end of the thirteenth century, all based on compass directions. From the time the Liber was written to the making of the oldest surviving portolan charts, there was a transitional period of several decades during which directions determined at sea started to be incorporated into nautical cartography, taking profit of the improved marine compasses.
In this paper I will show that many directions of the pelagic routes noted in the Liber could not have been measured with a marine compass because they are not affected by magnetic declination. This implies that they must have been determined using astronomical methods, for example, by taking the direction of the Pole Star or of the rising and setting of known stars as references. If most of the pelagic directions in the Liber were in fact taken from a chart, as indicated in the document, this means that a primitive type of portolan chart, not based on compass directions, was being developed at about 1200. This conclusion is consistent with the earliest extant references to the marine compass, which indicate that its use on board was exceptional during the last decades of the twelfth century.
It is further concluded that the genesis and technical evolution of the medieval portolan chart is a much longer and complex process than previously considered by the historians, who have based their analyses on the very few extant exemplars of the end of the thirteenth century, all based on compass directions. From the time the Liber was written to the making of the oldest surviving portolan charts, there was a transitional period of several decades during which directions determined at sea started to be incorporated into nautical cartography, taking profit of the improved marine compasses.
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The earliest known reference to a nautical chart is in a Latin manuscript of ca.1200, the Liber de existencia riveriarum et forma maris nostril mediterranei, written probably by a cleric in Pisa, with the explicit purpose of describing... more
The earliest known reference to a nautical chart is in a Latin manuscript of ca.1200, the Liber de existencia riveriarum et forma maris nostril mediterranei, written probably by a cleric in Pisa, with the explicit purpose of describing the Mediterranean Sea. In the prologue of the document, a reference is made to a chart that was constructed by the author and to how the information about the relative positions of the places in the Mediterranean was provided by the mariners and their rutters, as well as by the information the author could collect in his own voyages. Most part of the manuscript consists in a systematic listing of places and distances along the coast, organized in regional sections, each of them introduced by a short text indicating the orientation and size of the region. This information is complemented by a number of tracks connecting places situated in different regions, or between coastal places and islands (pelagic tracks), for which both distances and directions are provided. The analysis of these pelagic tracks suggests that most of the information was read from a chart while other may have been compiled from pilots’ rutters. An important point to note is that all directions are indicated in accordance to the eight classical winds, as in the oldest wind roses, to which eight intermediate ones were added. In this paper I will show that many directions of the pelagic routes noted in the Liber could not have been measured with a marine compass because they are not affected by magnetic declination. This implies that they must have been determined using astronomical methods, for example, by taking the direction of the Pole Star or of the rising and setting of known stars as references. If most of the pelagic directions in the Liber were in fact taken from a chart, as indicated in the document, this means that a primitive type of portolan chart, not based on compass directions, was being developed at about 1200. This conclusion is consistent with the earliest extant references to the marine compass, which indicate that its use on board was exceptional during the last decades of the twelfth century. It is further concluded that the genesis and technical evolution of the medieval portolan chart is a much longer and complex process than previously considered by the historians, who have based their analyses on the very few extant exemplars of the end of the thirteenth century, all based on compass directions. From the time the Liber was written to the making of the oldest surviving portolan charts, there was a transitional period of several decades during which directions determined at sea started to be incorporated into nautical cartography, taking profit of the improved marine compasses.
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In his acclaimed book Elements of Cartography, first published in 1969, the late American geographer Arthur Robinson stated that “maps are to be looked at while charts are to be worked on.” What Robinson intended to emphasize with this... more
In his acclaimed book Elements of Cartography, first published in 1969, the late American geographer Arthur Robinson stated that “maps are to be looked at while charts are to be worked on.” What Robinson intended to emphasize with this sentence is that maps and charts are constructed with different purposes in mind: while maps are basically a source of geographical information, which one can retrieve just by looking at them, charts were specifically designed to support the practice of navigation and facilitate graphical work.
Although Robinson’s definition is remarkably synthetic and expressive, it doesn’t tell the whole story, namely about the profound differences between these two cartographic paradigms. How those differences contributed to shape the history of maps and charts will be the subject of my presentation, which will focus on three different periods: the Middle Ages, when the first nautical charts were produced in the Mediterranean; the age of the great discoveries, when the newly discovered lands were first shown to the amazed eyes of the European nations through nautical charts; and the time of the Gerard Mercator, when the great Flemish cartographer proposed his famous projection to mariners.
I will show how the image of the world conveyed by nautical charts in each of these three periods could hardly be considered as truthful, as far as the shape and size of the lands were concerned. This was not because of the limitations of the surveying and charting methods of the time - although they had certainly a relevant influence - but owing to a critical difference regarding what should be understood by an accurate depiction of the Earth, in the eyes of geographers and navigators. In some instances these differences of opinion lead to conflict and resentment. In other occasions, they materialized into apparently unsolvable technical obstacles.
Only today can we see through the mist caused by the very subtle technical questions that the protagonists of the past couldn’t interpret correctly, and fully understand the reason for all the conflicts and misunderstandings: the intrinsically different nature of maps and charts.
Although Robinson’s definition is remarkably synthetic and expressive, it doesn’t tell the whole story, namely about the profound differences between these two cartographic paradigms. How those differences contributed to shape the history of maps and charts will be the subject of my presentation, which will focus on three different periods: the Middle Ages, when the first nautical charts were produced in the Mediterranean; the age of the great discoveries, when the newly discovered lands were first shown to the amazed eyes of the European nations through nautical charts; and the time of the Gerard Mercator, when the great Flemish cartographer proposed his famous projection to mariners.
I will show how the image of the world conveyed by nautical charts in each of these three periods could hardly be considered as truthful, as far as the shape and size of the lands were concerned. This was not because of the limitations of the surveying and charting methods of the time - although they had certainly a relevant influence - but owing to a critical difference regarding what should be understood by an accurate depiction of the Earth, in the eyes of geographers and navigators. In some instances these differences of opinion lead to conflict and resentment. In other occasions, they materialized into apparently unsolvable technical obstacles.
Only today can we see through the mist caused by the very subtle technical questions that the protagonists of the past couldn’t interpret correctly, and fully understand the reason for all the conflicts and misunderstandings: the intrinsically different nature of maps and charts.
Research Interests:
In his acclaimed book Elements of Cartography, first published in 1969, the late American geographer Arthur Robinson stated that “maps are to be looked at while charts are to be worked on.” What Robinson intended to emphasize with this... more
In his acclaimed book Elements of Cartography, first published in 1969, the late American geographer Arthur Robinson stated that “maps are to be looked at while charts are to be worked on.” What Robinson intended to emphasize with this sentence is that maps and charts are constructed with different purposes in mind: while maps are basically a source of geographical information, which one can retrieve just by looking at them, charts were specifically designed to support the practice of navigation and facilitate graphical work.
Although Robinson’s definition is remarkably synthetic and expressive, it doesn’t tell the whole story, namely about the profound differences between these two cartographic paradigms. How those differences contributed to shape the history of maps and charts will be the subject of my presentation, which will focus on three different periods: the Middle Ages, when the first nautical charts were produced in the Mediterranean; the age of the great discoveries, when the newly discovered lands were first shown to the amazed eyes of the European nations through nautical charts; and the time of the Gerard Mercator, when the great Flemish cartographer proposed his famous projection to mariners.
I will show how the image of the world conveyed by nautical charts in each of these three periods could hardly be considered as truthful, as far as the shape and size of the lands were concerned. This was not because of the limitations of the surveying and charting methods of the time - although they had certainly a relevant influence - but owing to a critical difference regarding what should be understood by an accurate depiction of the Earth, in the eyes of geographers and navigators. In some instances these differences of opinion lead to conflict and resentment. In other occasions, they materialized into apparently unsolvable technical obstacles.
Only today can we see through the mist caused by the very subtle technical questions that the protagonists of the past couldn’t interpret correctly, and fully understand the reason for all the conflicts and misunderstandings: the intrinsically different nature of maps and charts.
Although Robinson’s definition is remarkably synthetic and expressive, it doesn’t tell the whole story, namely about the profound differences between these two cartographic paradigms. How those differences contributed to shape the history of maps and charts will be the subject of my presentation, which will focus on three different periods: the Middle Ages, when the first nautical charts were produced in the Mediterranean; the age of the great discoveries, when the newly discovered lands were first shown to the amazed eyes of the European nations through nautical charts; and the time of the Gerard Mercator, when the great Flemish cartographer proposed his famous projection to mariners.
I will show how the image of the world conveyed by nautical charts in each of these three periods could hardly be considered as truthful, as far as the shape and size of the lands were concerned. This was not because of the limitations of the surveying and charting methods of the time - although they had certainly a relevant influence - but owing to a critical difference regarding what should be understood by an accurate depiction of the Earth, in the eyes of geographers and navigators. In some instances these differences of opinion lead to conflict and resentment. In other occasions, they materialized into apparently unsolvable technical obstacles.
Only today can we see through the mist caused by the very subtle technical questions that the protagonists of the past couldn’t interpret correctly, and fully understand the reason for all the conflicts and misunderstandings: the intrinsically different nature of maps and charts.
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Research Interests:
The map of Piri Reis (1513) is a precious monument of the Turkish and world cartographic heritage. Not because it is the most perfect and accurate exemplar of the Renaissance’s cartography (it is not) or because it depicts the Antarctica... more
The map of Piri Reis (1513) is a precious monument of the Turkish and world cartographic heritage. Not because it is the most perfect and accurate exemplar of the Renaissance’s cartography (it is not) or because it depicts the Antarctica with extraterrestrial accuracy (it does not) but because it contains the earliest extant representation of the Americas, illustrating with eloquence the conviction of Columbus about his arrival to the Orient. According to one of the map’s legends the lands shown on its western side were copied from a representation made by Cristopher Columbus himself, which was found in the hands of a sailor who accompanied the admiral on three of his exploration voyages. However extraordinary this claim seems it is confirmed by a careful exam of the map, as well as of the related contemporary sources, and has been supported by several historians who studied the manuscript.
The objective of the present paper is to situate the map of Piri Reis in the context of the European cartography of the sixteenth century from which, according to its author, the geographical information was compiled. To achieve such a goal a cartometric approach was adopted consisting in analyzing the geometry of the map and comparing the results with the typical geometries of the contemporary charts. Two specific cartometric tools were used: the interpolation of the geographical grid of meridians and parallels implicit in the representation, from which the cartographical model adopted for the different regions could be identified and a gross estimate of its accuracy could be made; and the assessment of the latitude accuracy of the map, from which finer conclusions about the cartographic standards and navigational accuracy could be drawn.
The results of this quantitative analysis, complemented with the available qualitative information, have permitted to better situate the map in the context of the contemporary cartography, to identify possible sources Piri Reis might have used in its construction and to have a sounder and more detailed idea about its navigational accuracy. Contradicting previous research, it was concluded that the Piri Reis’s map is not a latitude chart: the equator and the tropics are not represented, and the length of the degree of latitude implicit in the representation is identical to the one found in the portolan charts of the fifteenth century representing Western Europe. Furthermore the old thesis that this was the most accurate representation of the world made in the sixteenth century is not confirmed. On the contrary, if some difference can be found between this map and the Portuguese and Italian sources from which it was probably compiled, it is in the sense of a poorer detail and precision.
The objective of the present paper is to situate the map of Piri Reis in the context of the European cartography of the sixteenth century from which, according to its author, the geographical information was compiled. To achieve such a goal a cartometric approach was adopted consisting in analyzing the geometry of the map and comparing the results with the typical geometries of the contemporary charts. Two specific cartometric tools were used: the interpolation of the geographical grid of meridians and parallels implicit in the representation, from which the cartographical model adopted for the different regions could be identified and a gross estimate of its accuracy could be made; and the assessment of the latitude accuracy of the map, from which finer conclusions about the cartographic standards and navigational accuracy could be drawn.
The results of this quantitative analysis, complemented with the available qualitative information, have permitted to better situate the map in the context of the contemporary cartography, to identify possible sources Piri Reis might have used in its construction and to have a sounder and more detailed idea about its navigational accuracy. Contradicting previous research, it was concluded that the Piri Reis’s map is not a latitude chart: the equator and the tropics are not represented, and the length of the degree of latitude implicit in the representation is identical to the one found in the portolan charts of the fifteenth century representing Western Europe. Furthermore the old thesis that this was the most accurate representation of the world made in the sixteenth century is not confirmed. On the contrary, if some difference can be found between this map and the Portuguese and Italian sources from which it was probably compiled, it is in the sense of a poorer detail and precision.
Research Interests:
The map of Piri Reis (1513) is a precious monument of the Turkish and world cartographic heritage. Not because it is the most perfect and accurate exemplar of the Renaissance’s cartography (it is not) or because it depicts the Antarctica... more
The map of Piri Reis (1513) is a precious monument of the Turkish and world cartographic heritage. Not because it is the most perfect and accurate exemplar of the Renaissance’s cartography (it is not) or because it depicts the Antarctica with extraterrestrial accuracy (it does not) but because it contains the earliest extant representation of the Americas, illustrating with eloquence the conviction of Columbus about his arrival to the Orient. According to one of the map’s legends the lands shown on its western side were copied from a representation made by Cristopher Columbus himself, which was found in the hands of a sailor who accompanied the admiral on three of his exploration voyages. However extraordinary this claim seems it is confirmed by a careful exam of the map, as well as of the related contemporary sources, and has been supported by several historians who studied the manuscript.
The objective of the present paper is to situate the map of Piri Reis in the context of the European cartography of the sixteenth century from which, according to its author, the geographical information was compiled. To achieve such a goal a cartometric approach was adopted consisting in analyzing the geometry of the map and comparing the results with the typical geometries of the contemporary charts. Two specific cartometric tools were used: the interpolation of the geographical grid of meridians and parallels implicit in the representation, from which the cartographical model adopted for the different regions could be identified and a gross estimate of its accuracy could be made; and the assessment of the latitude accuracy of the map, from which finer conclusions about the cartographic standards and navigational accuracy could be drawn.
The results of this quantitative analysis, complemented with the available qualitative information, have permitted to better situate the map in the context of the contemporary cartography, to identify possible sources Piri Reis might have used in its construction and to have a sounder and more detailed idea about its navigational accuracy. Contradicting previous research, it was concluded that the Piri Reis’s map is not a latitude chart: the equator and the tropics are not represented, and the length of the degree of latitude implicit in the representation is identical to the one found in the portolan charts of the fifteenth century representing Western Europe. Furthermore the old thesis that this was the most accurate representation of the world made in the sixteenth century is not confirmed. On the contrary, if some difference can be found between this map and the Portuguese and Italian sources from which it was probably compiled, it is in the sense of a poorer detail and precision.
The objective of the present paper is to situate the map of Piri Reis in the context of the European cartography of the sixteenth century from which, according to its author, the geographical information was compiled. To achieve such a goal a cartometric approach was adopted consisting in analyzing the geometry of the map and comparing the results with the typical geometries of the contemporary charts. Two specific cartometric tools were used: the interpolation of the geographical grid of meridians and parallels implicit in the representation, from which the cartographical model adopted for the different regions could be identified and a gross estimate of its accuracy could be made; and the assessment of the latitude accuracy of the map, from which finer conclusions about the cartographic standards and navigational accuracy could be drawn.
The results of this quantitative analysis, complemented with the available qualitative information, have permitted to better situate the map in the context of the contemporary cartography, to identify possible sources Piri Reis might have used in its construction and to have a sounder and more detailed idea about its navigational accuracy. Contradicting previous research, it was concluded that the Piri Reis’s map is not a latitude chart: the equator and the tropics are not represented, and the length of the degree of latitude implicit in the representation is identical to the one found in the portolan charts of the fifteenth century representing Western Europe. Furthermore the old thesis that this was the most accurate representation of the world made in the sixteenth century is not confirmed. On the contrary, if some difference can be found between this map and the Portuguese and Italian sources from which it was probably compiled, it is in the sense of a poorer detail and precision.
Research Interests:
Em 1503 foi criada em Sevilha a Casa de la Contratación e, em 1508, Amerigo Vespúcio foi nomeado Piloto Mayor pela Coroa espanhola, tornando-se responsável pelo ensino dos pilotos, pela aprovação de instrumentos e cartas náuticas e pela... more
Em 1503 foi criada em Sevilha a Casa de la Contratación e, em 1508, Amerigo Vespúcio foi nomeado Piloto Mayor pela Coroa espanhola, tornando-se responsável pelo ensino dos pilotos, pela aprovação de instrumentos e cartas náuticas e pela construção de um mapa universal oficial designado por Padrón Real. Embora uma referência explícita seja feita, na mesma ordem real, ao uso de astrolábios e quadrantes, não existe qualquer evidência de que métodos astronómicos de navegação tenham sido utilizados pelos pilotos da Carrera de Indias durante o primeiro quartel do século XVI ou de que cartas de latitudes tenham sido produzidas pela Casa durante o mesmo período. Pelo contrário, a análise da parca cartografia da época claramente aponta para o facto de a navegação, para, e no Mar das Caraíbas se ter praticado, pelo menos até à viagem de Fernão de Magalhães, com recurso ao velho método do ponto de fantasia, e de as cartas que suportavam essa navegação se basearem no modelo da carta portulano.
Em 1519, preparava-se em Espanha a viagem de Fernão de Magalhães e um número significativo de especialistas portugueses – cosmógrafos, pilotos e cartógrafos – foi envolvido nessa preparação. Dois nomes são de realçar: o do cartógrafo Jorge Reinel que, em colaboração com seu pai Pedro, terá construído um planisfério náutico que viria a constituir o modelo da cartografia da Casa de Contratación; e o de Diogo Ribeiro, que seria nomeado alguns anos mais tarde cosmógrafo de sua majestade. Em conjunto com o cartógrafo Nuño García de Toreno, Diogo Ribeiro viria a assumir um papel de grande relevo na modernização da cartografia espanhola do Atlântico.
Nesta comunicação as inovações técnicas introduzidas na cartografia náutica da Casa de la Contratación no final do primeiro quartel do século XVI são descritas e discutidas. O estudo incide, sobretudo, sobre três cartas náuticas anónimas: o planisfério de c.1519 conhecido por Kunstmann IV (hoje perdido), atribuído a Jorge Reinel; o planisfério de 1525 usualmente conhecido por Salviatti, atribuído a Nuño García de Toreno; e o planisfério de 1525 conhecido por Castiglione, atribuído a Diogo Ribeiro. As seguintes inovações conferem a estas três cartas considerável relevância histórica: a graduação do Equador e a representação da totalidade do perímetro equatorial (Kunstmann IV); a representação do Arquipélago das Moluccas no hemisfério espanhol, segundo os termos do Tratado de Tordesilhas (Kunstmann IV); a correcção da distorção provocada pela declinação magnética na representação do Mediterrâneo e Mar Negro (Salviatti, Castiglione); a representação do Mar das Caraíbas na sua escala correcta e de acordo com as latitudes dos lugares (Salviatti, Castiglione); e a ilustração de instrumentos náuticos de observação astronómica (Castiglione).
Duas técnicas de análise cartométrica foram utilizadas neste estudo: a georreferenciação das cartas antigas, a partir da qual a malha geográfica de meridianos e paralelos que lhes está implícita pode ser interpolada e interpretada; e a quantificação dos erros de latitude, por comparação entre as latitudes dos lugares representados nas cartas, medidas nas respectivas escalas, e os valores verdadeiros.
O estudo conclui que a produção cartográfica da Casa de la Contratación sofreu um impulso considerável com a preparação e realização da viagem de Magalhães-Elcano. Este impulso foi propiciado pelas ambições imperiais da Coroa Espanhola e tornado possível pelo empenhamento de cartógrafos de origem portuguesa no processo. As três cartas analisadas são os exemplos espanhóis mais antigos de incorporação de latitudes na cartografia náutica e constituíram um modelo da Casa de la Contratación durante o século XVI.
Em 1519, preparava-se em Espanha a viagem de Fernão de Magalhães e um número significativo de especialistas portugueses – cosmógrafos, pilotos e cartógrafos – foi envolvido nessa preparação. Dois nomes são de realçar: o do cartógrafo Jorge Reinel que, em colaboração com seu pai Pedro, terá construído um planisfério náutico que viria a constituir o modelo da cartografia da Casa de Contratación; e o de Diogo Ribeiro, que seria nomeado alguns anos mais tarde cosmógrafo de sua majestade. Em conjunto com o cartógrafo Nuño García de Toreno, Diogo Ribeiro viria a assumir um papel de grande relevo na modernização da cartografia espanhola do Atlântico.
Nesta comunicação as inovações técnicas introduzidas na cartografia náutica da Casa de la Contratación no final do primeiro quartel do século XVI são descritas e discutidas. O estudo incide, sobretudo, sobre três cartas náuticas anónimas: o planisfério de c.1519 conhecido por Kunstmann IV (hoje perdido), atribuído a Jorge Reinel; o planisfério de 1525 usualmente conhecido por Salviatti, atribuído a Nuño García de Toreno; e o planisfério de 1525 conhecido por Castiglione, atribuído a Diogo Ribeiro. As seguintes inovações conferem a estas três cartas considerável relevância histórica: a graduação do Equador e a representação da totalidade do perímetro equatorial (Kunstmann IV); a representação do Arquipélago das Moluccas no hemisfério espanhol, segundo os termos do Tratado de Tordesilhas (Kunstmann IV); a correcção da distorção provocada pela declinação magnética na representação do Mediterrâneo e Mar Negro (Salviatti, Castiglione); a representação do Mar das Caraíbas na sua escala correcta e de acordo com as latitudes dos lugares (Salviatti, Castiglione); e a ilustração de instrumentos náuticos de observação astronómica (Castiglione).
Duas técnicas de análise cartométrica foram utilizadas neste estudo: a georreferenciação das cartas antigas, a partir da qual a malha geográfica de meridianos e paralelos que lhes está implícita pode ser interpolada e interpretada; e a quantificação dos erros de latitude, por comparação entre as latitudes dos lugares representados nas cartas, medidas nas respectivas escalas, e os valores verdadeiros.
O estudo conclui que a produção cartográfica da Casa de la Contratación sofreu um impulso considerável com a preparação e realização da viagem de Magalhães-Elcano. Este impulso foi propiciado pelas ambições imperiais da Coroa Espanhola e tornado possível pelo empenhamento de cartógrafos de origem portuguesa no processo. As três cartas analisadas são os exemplos espanhóis mais antigos de incorporação de latitudes na cartografia náutica e constituíram um modelo da Casa de la Contratación durante o século XVI.
Research Interests:
Em 1503 foi criada em Sevilha a Casa de la Contratación e, em 1508, Amerigo Vespúcio foi nomeado Piloto Mayor pela Coroa espanhola, tornando-se responsável pelo ensino dos pilotos, pela aprovação de instrumentos e cartas náuticas e pela... more
Em 1503 foi criada em Sevilha a Casa de la Contratación e, em 1508, Amerigo Vespúcio foi nomeado Piloto Mayor pela Coroa espanhola, tornando-se responsável pelo ensino dos pilotos, pela aprovação de instrumentos e cartas náuticas e pela construção de um mapa universal oficial designado por Padrón Real. Embora uma referência explícita seja feita, na mesma ordem real, ao uso de astrolábios e quadrantes, não existe qualquer evidência de que métodos astronómicos de navegação tenham sido utilizados pelos pilotos da Carrera de Indias durante o primeiro quartel do século XVI ou de que cartas de latitudes tenham sido produzidas pela Casa durante o mesmo período. Pelo contrário, a análise da parca cartografia da época claramente aponta para o facto de a navegação, para, e no Mar das Caraíbas se ter praticado, pelo menos até à viagem de Fernão de Magalhães, com recurso ao velho método do ponto de fantasia, e de as cartas que suportavam essa navegação se basearem no modelo da carta portulano.
Em 1519, preparava-se em Espanha a viagem de Fernão de Magalhães e um número significativo de especialistas portugueses – cosmógrafos, pilotos e cartógrafos – foi envolvido nessa preparação. Dois nomes são de realçar: o do cartógrafo Jorge Reinel que, em colaboração com seu pai Pedro, terá construído um planisfério náutico que viria a constituir o modelo da cartografia da Casa de Contratación; e o de Diogo Ribeiro, que seria nomeado alguns anos mais tarde cosmógrafo de sua majestade. Em conjunto com o cartógrafo Nuño García de Toreno, Diogo Ribeiro viria a assumir um papel de grande relevo na modernização da cartografia espanhola do Atlântico.
Nesta comunicação as inovações técnicas introduzidas na cartografia náutica da Casa de la Contratación no final do primeiro quartel do século XVI são descritas e discutidas. O estudo incide, sobretudo, sobre três cartas náuticas anónimas: o planisfério de c.1519 conhecido por Kunstmann IV (hoje perdido), atribuído a Jorge Reinel; o planisfério de 1525 usualmente conhecido por Salviatti, atribuído a Nuño García de Toreno; e o planisfério de 1525 conhecido por Castiglione, atribuído a Diogo Ribeiro. As seguintes inovações conferem a estas três cartas considerável relevância histórica: a graduação do Equador e a representação da totalidade do perímetro equatorial (Kunstmann IV); a representação do Arquipélago das Moluccas no hemisfério espanhol, segundo os termos do Tratado de Tordesilhas (Kunstmann IV); a correcção da distorção provocada pela declinação magnética na representação do Mediterrâneo e Mar Negro (Salviatti, Castiglione); a representação do Mar das Caraíbas na sua escala correcta e de acordo com as latitudes dos lugares (Salviatti, Castiglione); e a ilustração de instrumentos náuticos de observação astronómica (Castiglione).
Duas técnicas de análise cartométrica foram utilizadas neste estudo: a georreferenciação das cartas antigas, a partir da qual a malha geográfica de meridianos e paralelos que lhes está implícita pode ser interpolada e interpretada; e a quantificação dos erros de latitude, por comparação entre as latitudes dos lugares representados nas cartas, medidas nas respectivas escalas, e os valores verdadeiros.
O estudo conclui que a produção cartográfica da Casa de la Contratación sofreu um impulso considerável com a preparação e realização da viagem de Magalhães-Elcano. Este impulso foi propiciado pelas ambições imperiais da Coroa Espanhola e tornado possível pelo empenhamento de cartógrafos de origem portuguesa no processo. As três cartas analisadas são os exemplos espanhóis mais antigos de incorporação de latitudes na cartografia náutica e constituíram um modelo da Casa de la Contratación durante o século XVI.
Em 1519, preparava-se em Espanha a viagem de Fernão de Magalhães e um número significativo de especialistas portugueses – cosmógrafos, pilotos e cartógrafos – foi envolvido nessa preparação. Dois nomes são de realçar: o do cartógrafo Jorge Reinel que, em colaboração com seu pai Pedro, terá construído um planisfério náutico que viria a constituir o modelo da cartografia da Casa de Contratación; e o de Diogo Ribeiro, que seria nomeado alguns anos mais tarde cosmógrafo de sua majestade. Em conjunto com o cartógrafo Nuño García de Toreno, Diogo Ribeiro viria a assumir um papel de grande relevo na modernização da cartografia espanhola do Atlântico.
Nesta comunicação as inovações técnicas introduzidas na cartografia náutica da Casa de la Contratación no final do primeiro quartel do século XVI são descritas e discutidas. O estudo incide, sobretudo, sobre três cartas náuticas anónimas: o planisfério de c.1519 conhecido por Kunstmann IV (hoje perdido), atribuído a Jorge Reinel; o planisfério de 1525 usualmente conhecido por Salviatti, atribuído a Nuño García de Toreno; e o planisfério de 1525 conhecido por Castiglione, atribuído a Diogo Ribeiro. As seguintes inovações conferem a estas três cartas considerável relevância histórica: a graduação do Equador e a representação da totalidade do perímetro equatorial (Kunstmann IV); a representação do Arquipélago das Moluccas no hemisfério espanhol, segundo os termos do Tratado de Tordesilhas (Kunstmann IV); a correcção da distorção provocada pela declinação magnética na representação do Mediterrâneo e Mar Negro (Salviatti, Castiglione); a representação do Mar das Caraíbas na sua escala correcta e de acordo com as latitudes dos lugares (Salviatti, Castiglione); e a ilustração de instrumentos náuticos de observação astronómica (Castiglione).
Duas técnicas de análise cartométrica foram utilizadas neste estudo: a georreferenciação das cartas antigas, a partir da qual a malha geográfica de meridianos e paralelos que lhes está implícita pode ser interpolada e interpretada; e a quantificação dos erros de latitude, por comparação entre as latitudes dos lugares representados nas cartas, medidas nas respectivas escalas, e os valores verdadeiros.
O estudo conclui que a produção cartográfica da Casa de la Contratación sofreu um impulso considerável com a preparação e realização da viagem de Magalhães-Elcano. Este impulso foi propiciado pelas ambições imperiais da Coroa Espanhola e tornado possível pelo empenhamento de cartógrafos de origem portuguesa no processo. As três cartas analisadas são os exemplos espanhóis mais antigos de incorporação de latitudes na cartografia náutica e constituíram um modelo da Casa de la Contratación durante o século XVI.
Research Interests:
Little is known about the sources used by Mercator to compile his world map of 1569. According to one of the map legends, Castilian and Portuguese charts were compared with each other as well as with travel accounts, and it was “from an... more
Little is known about the sources used by Mercator to compile his world map of 1569. According to one of the map legends, Castilian and Portuguese charts were compared with each other as well as with travel accounts, and it was “from an equitable conciliation of all these documents that the dimensions and situations of the land are [were] given here as exactly as possible”. However Mercator didn’t say anything about the methods he used to convert those pieces of information into a form that could be used to draw the map, that is, into a list of latitudes and longitudes. While the determination of latitude by astronomical observations was already a routine process in Mercator’s time, that was not the case of the determination of longitude. Although the basic principles and methodologies were known since antiquity, the inaccuracy of the astronomical tables and the difficulties associated with the observations made the results not to be trusted for navigational purposes.
At the time Mercator engraved his world map navigational charts were constructed using the latitudes of the places and the magnetic courses connecting them. Before this information could be used in the new map it should be first transformed in such a way that the places were represented according to their longitude differences. Whether Mercator performed such transformation or just considered that the longitudes were approximately correct is unknown. In order to shed some light into the question a cartometric analysis of Mercator’s world map of 1569 was made focused on its navigational accuracy.
Three independent components of the map’s accuracy are considered, all affecting its quality as a navigational chart: the accuracy of the graticule, which is measured by the agreement between the position of the meridians and parallels with the theoretical grid of the cylindrical conformal projection; the absolute positional accuracy of the places, that is, the accuracy of their latitudes and longitudes as measured on the scales of the map and then compared with the exact values; and the relative positional accuracy of the places, whose most important component is the accuracy of the rhumb-line directions connecting them.
It is a well-known fact that the Mercator projection was mostly ignored by the pilots at the time it was proposed and that its full adoption by marine navigation had still to wait some two hundred years, until more was known about the spatial distribution of magnetic declination and effective methods for finding longitude were developed. If the resistance of the pilots had anything to do with the lack of navigational accuracy of the map is a possibility that should be also investigated.
At the time Mercator engraved his world map navigational charts were constructed using the latitudes of the places and the magnetic courses connecting them. Before this information could be used in the new map it should be first transformed in such a way that the places were represented according to their longitude differences. Whether Mercator performed such transformation or just considered that the longitudes were approximately correct is unknown. In order to shed some light into the question a cartometric analysis of Mercator’s world map of 1569 was made focused on its navigational accuracy.
Three independent components of the map’s accuracy are considered, all affecting its quality as a navigational chart: the accuracy of the graticule, which is measured by the agreement between the position of the meridians and parallels with the theoretical grid of the cylindrical conformal projection; the absolute positional accuracy of the places, that is, the accuracy of their latitudes and longitudes as measured on the scales of the map and then compared with the exact values; and the relative positional accuracy of the places, whose most important component is the accuracy of the rhumb-line directions connecting them.
It is a well-known fact that the Mercator projection was mostly ignored by the pilots at the time it was proposed and that its full adoption by marine navigation had still to wait some two hundred years, until more was known about the spatial distribution of magnetic declination and effective methods for finding longitude were developed. If the resistance of the pilots had anything to do with the lack of navigational accuracy of the map is a possibility that should be also investigated.
Research Interests:
Little is known about the sources used by Mercator to compile his world map of 1569. According to one of the map legends, Castilian and Portuguese charts were compared with each other as well as with travel accounts, and it was “from an... more
Little is known about the sources used by Mercator to compile his world map of 1569. According to one of the map legends, Castilian and Portuguese charts were compared with each other as well as with travel accounts, and it was “from an equitable conciliation of all these documents that the dimensions and situations of the land are [were] given here as exactly as possible”. However Mercator didn’t say anything about the methods he used to convert those pieces of information into a form that could be used to draw the map, that is, into a list of latitudes and longitudes. While the determination of latitude by astronomical observations was already a routine process in Mercator’s time, that was not the case of the determination of longitude. Although the basic principles and methodologies were known since antiquity, the inaccuracy of the astronomical tables and the difficulties associated with the observations made the results not to be trusted for navigational purposes.
At the time Mercator engraved his world map navigational charts were constructed using the latitudes of the places and the magnetic courses connecting them. Before this information could be used in the new map it should be first transformed in such a way that the places were represented according to their longitude differences. Whether Mercator performed such transformation or just considered that the longitudes were approximately correct is unknown. In order to shed some light into the question a cartometric analysis of Mercator’s world map of 1569 was made focused on its navigational accuracy.
Three independent components of the map’s accuracy are considered, all affecting its quality as a navigational chart: the accuracy of the graticule, which is measured by the agreement between the position of the meridians and parallels with the theoretical grid of the cylindrical conformal projection; the absolute positional accuracy of the places, that is, the accuracy of their latitudes and longitudes as measured on the scales of the map and then compared with the exact values; and the relative positional accuracy of the places, whose most important component is the accuracy of the rhumb-line directions connecting them.
It is a well-known fact that the Mercator projection was mostly ignored by the pilots at the time it was proposed and that its full adoption by marine navigation had still to wait some two hundred years, until more was known about the spatial distribution of magnetic declination and effective methods for finding longitude were developed. If the resistance of the pilots had anything to do with the lack of navigational accuracy of the map is a possibility that should be also investigated.
At the time Mercator engraved his world map navigational charts were constructed using the latitudes of the places and the magnetic courses connecting them. Before this information could be used in the new map it should be first transformed in such a way that the places were represented according to their longitude differences. Whether Mercator performed such transformation or just considered that the longitudes were approximately correct is unknown. In order to shed some light into the question a cartometric analysis of Mercator’s world map of 1569 was made focused on its navigational accuracy.
Three independent components of the map’s accuracy are considered, all affecting its quality as a navigational chart: the accuracy of the graticule, which is measured by the agreement between the position of the meridians and parallels with the theoretical grid of the cylindrical conformal projection; the absolute positional accuracy of the places, that is, the accuracy of their latitudes and longitudes as measured on the scales of the map and then compared with the exact values; and the relative positional accuracy of the places, whose most important component is the accuracy of the rhumb-line directions connecting them.
It is a well-known fact that the Mercator projection was mostly ignored by the pilots at the time it was proposed and that its full adoption by marine navigation had still to wait some two hundred years, until more was known about the spatial distribution of magnetic declination and effective methods for finding longitude were developed. If the resistance of the pilots had anything to do with the lack of navigational accuracy of the map is a possibility that should be also investigated.
Research Interests:
In his ‘Treatise in defense of the nautical chart’ (1537), the Portuguese mathematician Pedro Nunes refers to the exaggerated longitudinal distance between Lisbon and India, as depicted in the contemporary charts. According to Nunes, the... more
In his ‘Treatise in defense of the nautical chart’ (1537), the Portuguese mathematician Pedro Nunes refers to the exaggerated longitudinal distance between Lisbon and India, as depicted in the contemporary charts. According to Nunes, the distortion was caused by the pilots, who represented as straight what had been ‘sailed with so many detours’. Some twenty five years later (c. 1560) the knight and cartographer Lopo Homem, in a note written to King João III, complains about the new cartographic pattern ordered by the cosmographer-major Pedro Nunes, which was ‘wildly distant from all truth and navigational science’. In 1571, in his De rebus Emmanuelis Regis Lusitaniae, the historian Jerónimo Osório describes how some learned men, instructed by Pedro Nunes, have determined the longitudinal distance between Lisbon and the mouth of the Indian River using astronomical methods. Who is right and wrong in this dispute? Pedro Nunes, who invokes the mathematical sciences to defend his interpretation of geographical reality? Or Lopo Homem, who represents the view of the pilots and supports his arguments with practical considerations? In this paper the two different views are analyzed technically, taking into account the charts and navigational methods of the sixteenth century.
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In his ‘Treatise in defense of the nautical chart’ (1537), the Portuguese mathematician Pedro Nunes refers to the exaggerated longitudinal distance between Lisbon and India, as depicted in the contemporary charts. According to Nunes, the... more
In his ‘Treatise in defense of the nautical chart’ (1537), the Portuguese mathematician Pedro Nunes refers to the exaggerated longitudinal distance between Lisbon and India, as depicted in the contemporary charts. According to Nunes, the distortion was caused by the pilots, who represented as straight what had been ‘sailed with so many detours’. Some twenty five years later (c. 1560) the knight and cartographer Lopo Homem, in a note written to King João III, complains about the new cartographic pattern ordered by the cosmographer-major Pedro Nunes, which was ‘wildly distant from all truth and navigational science’. In 1571, in his De rebus Emmanuelis Regis Lusitaniae, the historian Jerónimo Osório describes how some learned men, instructed by Pedro Nunes, have determined the longitudinal distance between Lisbon and the mouth of the Indian River using astronomical methods. Who is right and wrong in this dispute? Pedro Nunes, who invokes the mathematical sciences to defend his interpretation of geographical reality? Or Lopo Homem, who represents the view of the pilots and supports his arguments with practical considerations? In this paper the two different views are analyzed technically, taking into account the charts and navigational methods of the sixteenth century.
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The MEDEA-CHART database was created as a tool to assist in the study of medieval and early modern nautical charts. The database also aims to facilitate access to nautical charts for both the scientific community and all members of the... more
The MEDEA-CHART database was created as a tool to assist in the study of medieval and early modern nautical charts. The database also aims to facilitate access to nautical charts for both the scientific community and all members of the public. In short, we collect dispersed information on nautical charts and compile it on a single online platform, available to anyone for free. The development process started about a year and a half ago and is ongoing. MEDEA-CHART project members have an active role in the process of defining and testing newly database features, ensuring that the system reaches the level of usability required of a research tool. As development is still in progress, new features are expected to arrive in the future. We would like to extend our gratitude to Dick Pflederer for allowing the use of his census. This resource has been invaluable in populating the database. As a developer, I have found this work particularly interesting, as I have had to collaborate with researchers and learn new tools to continue to improve the system. The challenge of developing a user-friendly and innovative tool for the study of cartography is tremendously motivating. The MEDEA-CHART database can be accessed for free at https://medea.fc.ul.pt. Ricardo Vaz
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In this thesis a methodology for the systematic geometric analysis and modeling of pre-Mercator nautical charts is proposed and tested, aiming at contributing to better understand their geometric properties and methods of construction.... more
In this thesis a methodology for the systematic geometric analysis and modeling of pre-Mercator nautical charts is proposed and tested, aiming at contributing to better understand their geometric properties and methods of construction. The suggested approach involves the application of a series of cartometric techniques: georeferenc-ing, on the basis of a sample of control points of known geographic coordinates; the interpolation of the geographical graticules implicit to the representations; the assessment of scales of distance and latitude; the assessment of the navigational accura-cy, by comparing the latitudes, directions and distances measured on the charts with the corresponding exact values, affected by magnetic declination; and the identifica-tion of the routes underlying the charts’ construction. A numerical model was devel-oped using the concept of ‘multimensional scaling’, here generalized to distances and directions measured on a spherical Earth, to simulate the main geometric features of the charts. To estimate the spatial distribution of the magnetic declination in various times two sources were used: the historical observations made by D. João de Castro in 1538 and 1541, and a recent geomagnetic model.
The methodology of cartometric analysis proposed in the thesis proved to be effective and accurate. Five Portuguese charts from circa 1471 to 1504 were analyzed using the full set of techniques mentioned above. The analysis revealed the coexistence of two distinct cartographic models in the nautical cartography of the time: the ‘portolan-chart’ model, based on magnetic directions and estimated distances, used to represent the Mediterranean, the Black Sea and Western Europe; and the ‘latitude chart’ model, based on astronomically-observed latitudes, used to represent Brazil and Africa. His-torically relevant conclusions about the construction details and the sources used in the compilation of the charts were drawn. Some of the most interesting refer to the Cantino planisphere, whose cartographic information was found to be compiled from several sources of distinct origins, times and accuracies. Certain peculiarities of its geometry, especially the location of Greenland, the distorted shape of Africa and the orientation of the Mediterranean, are shown to be the result of the navigational and charting methods of the time, under the influence of magnetic declination. Concerning the standards adopted in the Iberian pre-Mercator nautical cartography, important conclusions were drawn on the type of distance scales and the length of the degree of latitude, some of them contradicting the results of previous studies. One of the most interesting is that the various lengths of the degree adopted in the charts of the time had little navigational impact, being only an echo of the traditional models of the Earth and of the political disputes between Portugal and Spain.
The numerical model developed for the purpose of simulating the main geometric features of the charts proved to be a valuable research tool and was used, not only for producing the simulations presented in the thesis, but also for quickly assessing the influence of the various factors affecting the geometry of the charts.
The variety and richness of the conclusions drawn in the present research eloquently confirm the utility and effectiveness of the proposed methodology. Hopefully they will arouse the interest of others and help recognizing the need for a multidisciplinary ap-proach in the study of old nautical charts.
The methodology of cartometric analysis proposed in the thesis proved to be effective and accurate. Five Portuguese charts from circa 1471 to 1504 were analyzed using the full set of techniques mentioned above. The analysis revealed the coexistence of two distinct cartographic models in the nautical cartography of the time: the ‘portolan-chart’ model, based on magnetic directions and estimated distances, used to represent the Mediterranean, the Black Sea and Western Europe; and the ‘latitude chart’ model, based on astronomically-observed latitudes, used to represent Brazil and Africa. His-torically relevant conclusions about the construction details and the sources used in the compilation of the charts were drawn. Some of the most interesting refer to the Cantino planisphere, whose cartographic information was found to be compiled from several sources of distinct origins, times and accuracies. Certain peculiarities of its geometry, especially the location of Greenland, the distorted shape of Africa and the orientation of the Mediterranean, are shown to be the result of the navigational and charting methods of the time, under the influence of magnetic declination. Concerning the standards adopted in the Iberian pre-Mercator nautical cartography, important conclusions were drawn on the type of distance scales and the length of the degree of latitude, some of them contradicting the results of previous studies. One of the most interesting is that the various lengths of the degree adopted in the charts of the time had little navigational impact, being only an echo of the traditional models of the Earth and of the political disputes between Portugal and Spain.
The numerical model developed for the purpose of simulating the main geometric features of the charts proved to be a valuable research tool and was used, not only for producing the simulations presented in the thesis, but also for quickly assessing the influence of the various factors affecting the geometry of the charts.
The variety and richness of the conclusions drawn in the present research eloquently confirm the utility and effectiveness of the proposed methodology. Hopefully they will arouse the interest of others and help recognizing the need for a multidisciplinary ap-proach in the study of old nautical charts.