Charting the Age of Discovery: The Cartography of Early Global Exploration

The second great contribution to the revival of cartography was made by the leaders of overseas expansion: the seamen of many nations — Italian, Portuguese, Spanish, French, Dutch and English — who, in little more than a century, opened up the oceans of the world, with the partial exception of the Pacific, and provided chartmakers with the data for the maps of their coastlines.

The outstanding stages in this progress are: the rounding of the southern promontory of Africa by Bartholomew Dias in 1487; the landfall of Columbus in the West Indies in 1492; the attainment of India by Vasco da Gama in 1498; the discovery of Brazil by Pedro Álvares Cabral in 1500; the capture of Malacca by Afonso de Albuquerque in 1511; the arrival of the first Portuguese in the Moluccas in the following year; and the circumnavigation of the globe by Magellan’s expedition (1519–1522).

Navigation Methods of the Pioneers

To judge the standard of accuracy of these charts, we must glance rapidly at the methods of navigation practiced by these pioneer seamen.

At the outset of their African voyages, the Portuguese pilots followed the same methods of navigation as the seafaring peoples of the Mediterranean.

From the marine charts they ascertained the direction, or rhumb, of the proposed voyage, and also its distance.

With the aid of the mariner’s compass and primitive methods of determining the vessel’s speed, they tried to keep as close as possible to this track, estimating their position daily.

Coastwise Sailing and Use of Landmarks

In the Mediterranean, voyages were largely — but not exclusively — a matter of coastwise sailing, so much reliance was also placed on acquired knowledge of local winds and currents and on the ability to recognize prominent coastal landmarks: a bold headland, a group of islets, or a distinctively shaped mountain.

Pilots in the Mediterranean therefore rarely troubled to determine their latitude, partly because the latitudinal range was relatively small and partly because the degree of accuracy of their observations was not high.

Challenges on the Atlantic and the Turn to Astronomical Methods

When the Portuguese embarked upon the waters of the Atlantic and made their way southwards along the African coasts, they encountered different conditions.

There was no body of traditional seafarers’ lore to draw upon regarding winds and currents; familiar landmarks were lacking on the coasts, which were often characterless for considerable stretches and fringed by unseen hazards.

A hostile population discouraged unnecessary approaches, and there was the possibility of being driven off course into the open ocean. They were also ranging through many degrees of latitude.

In these circumstances the pilots turned to the determination of latitude, at first by observing the altitude of the Pole Star.

Later, as the vessels pressed further south and the Pole Star sank lower in the sky, latitude was obtained from the midday altitude of the sun with the help of tables of declination.

These observations were made with the astrolabe — gradually simplified from the landsman’s type — and with the quadrant, a less cumbrous instrument.

Corrections and Tables for Latitude

Since the Pole Star does not coincide exactly with the celestial pole, it was necessary to apply a correction to its observed altitude to obtain the latitude.

The correction depended on the time of the observation, which could be obtained from the position of Ursa Major in its orbit around the Pole.

A set of simple instructions, known as “The Regiment of the North,” was therefore drawn up, giving the correction to be applied for certain positions of the “Guards.”

For the corrections to be applied to the sun’s midday altitude, a primitive table had probably been worked out by 1456.

Later, José Vizinho, utilizing the work of the Jewish astronomer Abraham Zacuto, calculated a table for each day of the leap year March 1483–February 1484; this was used by Bartolomeu Dias in his famous voyage.

Later still, Zacuto assisted in preparing a perpetual almanac for the voyage of Vasco da Gama.

Chronology of Scientific Aids and Chart Features

These scientific aids were provided relatively late in the fifteenth century; the first recorded use of the quadrant at sea dates from 1460.

It is not until the early years of the sixteenth century that scales of latitude appear on marine charts. Until then, the charts recording the Portuguese advance along the African coasts continued to display features of the Mediterranean portolan charts.

Since the coasts they were charting ran mostly in a southerly direction, this was not at first a major difficulty, though the influence of magnetic variation was not appreciated.

It had been observed on land, but its calculation at sea was not seriously undertaken until the next century.

Convergence of Meridians and Chart Accuracy

When it became necessary to chart accurately a number of points situated, for example, on each side of the Atlantic and extending through many degrees of latitude, the neglect of the convergence of meridians rendered the old type of chart extremely inaccurate.

The task before the pilots at this stage was still largely to set down distance and direction as accurately as possible. But when we examine surviving charts — for example Andrea Bianco’s at the beginning of the period (1448) and Grazioso Benincasa’s chart of discoveries some distance beyond Sierra Leone (1468) — we must conclude either that they were very carelessly assembled from sectional charts, or that accuracy of distances was forfeited for some other purpose.

Benincasa’s chart portrays the coast on a scale that increases steadily southwards, the scale of the most southerly portion being nearly four times that of the northern.

The northern portion of the coastline is featureless in contrast to the estuaries and islands further south, and it is possible that the diversified coast was deliberately drawn on a larger scale.

Bianco, Benincasa and Use of Landmarks

A similar variation in scale and emphasis on prominent features is characteristic also of Bianco’s chart.

In the brief reference above to methods of navigation, the extent to which landmarks were employed in coastwise sailing was pointed out, and by this enlargement of scale features were made more easily recognizable.

The descriptive names used on the charts served the same purpose.

Latitude Fixing and “Running Down the Easting”

When the latitudes of a number of places on the African coast had been fixed, it became less necessary to emphasize particular stretches in this way, for the navigators were not tied to coastwise sailing.

In rounding the Cape, for example, it was the practice to sail southwards as rapidly as possible to the necessary parallel of latitude and then to turn eastwards, keeping as close as possible to the parallel (“running down the easting”). If through navigational errors the African coast were sighted north of the Cape, it was a simple matter to coast southwards.

To assist in determining their latitude, navigators were provided with tables known as “Rules of the Leagues,” which simply stated the number of leagues it was necessary to sail on various bearings in order to make good one degree of latitude, north or south (i.e. the hypotenuse of a right-angled triangle of which one other side equals 1° or ~70 miles).

Longitude and Dead Reckoning

Since the astronomical determination of longitude was a process of great complexity before the invention of accurate timekeepers, all east–west distances depended upon dead reckoning alone.

From the courses and distances run, it was possible by the application of the “Rules” to calculate each day’s sailing and ultimately the total voyage.

Given the length of a degree of longitude at various latitudes, it was possible to arrive at an approximate figure for the difference of longitude.

It is necessary to keep these considerations in mind when discussing the accuracy of the charts which record the great discoveries.

Survival and Scarcity of Early Cartographic Material

All these maritime achievements, in the east and in the west, were accomplished within thirty-five years, and one might expect the cartographic output for this period to be large.

Actually, despite the momentous events to be recorded, it is not great—or, to be more accurate, the material that has survived is relatively slight.

No original chart from the period 1487 to 1500 has been preserved.

The nearest is a copy of a chart of the western African coasts to the neighbourhood of the Cape of Good Hope contained in the collection generally known by the name of the copyist, Soligo, which was probably made about 1490 (B.M. Egerton 73).

The representation of Africa in the globe of Martin Behaim and the map of Henricus Martellus may possibly be based on contemporary charts at second or third hand—but otherwise this decade is cartographically a blank.

If the period is extended to 1510, the number of survivals is still relatively small; the more important are the world charts, or planispheres, of La Cosa, Cantino, and Canerio; the so-called King‑Hamy planisphere; and three regional charts, one of which is certainly by Pedro Reinel.

To these may be added the crude sketch of the northern coast of Hispaniola attributed to Columbus, and the diagrammatic representation of the world incorporating the new discoveries by Bartholomeo Columbus.

Secondary Material and Delay in Publication

As will be seen, the secondary material also is not large. The time-lag in the appearance of maps of the new discoveries to satisfy public interest is shown by the fact that no map of any part of the New World or of the Portuguese discoveries in the east appeared in a Ptolemy atlas until 1507.

As it is known from contemporary records that many charts were made during this period, the question arises why so few have survived.

The reason is partly that in the early years charts were in high demand by navigators and would consequently be widely dispersed and rapidly worn out or lost.

As to Portuguese charts, a large number was undoubtedly lost in the Lisbon earthquake of 1755.

As a widespread interest in the discoveries only developed slowly, there is also little secondary material. Vasco da Gama’s opening of the sea route to India in 1498 and Vespucci’s account of the New World (popularized by Waldseemüller’s Introductio Cosmographiae) were the events that really caught popular attention.

The first collection of voyages, which brought both the East and West Indian voyages together, appeared only in 1506. Portuguese historians have argued that this was the result of an official policy of secrecy.

It is recorded, for example, that King John II imposed a ban on the circulation of charts.

Since, however, pilots and cartographers passed from the service of one monarch to that of another apparently without incurring much odium, it must have been difficult to keep charts secret for long, and we shall see that, after 1500 at least, a few copies of charts recording the discoveries were available in Italy.

Columbus Materials and Sketches

In keeping with the general paucity of cartographic material relating to the earliest years of the discoveries, only two small items have survived which can with any certainty be ascribed either to Christopher Columbus or to his brother Bartolomeo, a chartmaker by profession. In the archives of the Duke of Alba in Madrid there is a hasty outline sketch of the north and north-western coastline of Cuba, on which occurs the name “nativida,” for La Natividad, the first settlement in the New World, which Columbus had founded on his first voyage.

This is ascribed to Christopher. The second consists of three marginal sketches in a copy of Columbus’s letter of July 1503 describing his fourth voyage, preserved in the National Library, Florence.

From this we learn that a regular survey of the Central American coast was carried out by Bartolomeo.

The sketch maps ascribed to him form an outline of the world between the tropics and are of particular interest as they illustrate very clearly Columbus’s ideas on the relationship of his discoveries to south‑eastern Asia.

The north coast of South America is prolonged westward before it joins that of Central America, and the latter is joined to the Asian coastline of Ptolemy in the neighbourhood of Cattigara.

This synthesis required the placing of Central America 120° of longitude to the west of Cape Verde.

Possible Columbus Map and Early New World Charts

Some years ago Charles de la Roncière drew attention to a circular world map in the Bibliothèque nationale, Paris, which he argued had been prepared at Columbus’s direction for presentation to the Spanish sovereigns.

La Roncière’s arguments have been strongly controverted; in any case, the map ante-dates the first voyage and does not throw any significant light upon Columbus’s aims.

There is some doubt as to which is the earliest extant chart to show any of the discoveries in the New World.

This is either a chart by La Cosa or an anonymous one, known by the name Cantino, which can be definitely dated 1502.

The La Cosa chart bears the date 1500, but this has been challenged. We may accept it for the chart as a whole, though some additions were probably made to it later, for G. E. Nunn’s arguments for dating it c. 1508 are not entirely convincing.

Juan de la Cosa’s Chart

Juan de la Cosa, an expert Biscayan navigator and owner of the Santa María, accompanied Columbus on his first two voyages. He later made further voyages to the American continent and is known to have drawn several other charts since lost.

The map, 180 x 96 cm, somewhat crudely drawn on parchment, has suffered considerable damage. On the western margin, below a drawing of St. Christopher in the neck of the skin, is the inscription “Juan de la Cosa la fizo en el puerto de Santa María en año de 1500.”

The chart is in the style of earlier marine charts, with compass roses and direction lines.

The scale is given by a line of dots, unnumbered and unexplained; the distance between the points, however, is apparently intended to represent fifty miles.

The northern tropic and the equator are drawn, but degrees of latitude or longitude are not indicated.

In the west are the discoveries of Cabot in the north and of Columbus and the Spaniards in the West Indies and along the north-eastern coasts of South America. The Bahamas group is shown with some accuracy but necessarily on a small scale. It includes the island Guanahani, alternatively known as San Salvador and now identified with Watling Island.

No special emphasis is given to this memorable locality. Off the South American coast is a large “island discovered by the Portuguese,” representing Cabral’s discovery of Brazil in 1500.

The chartmaker appears to have considered the American coastline to be continuous from north to south, but this cannot be asserted with certainty, as the Central American area is hidden by the drawing of St. Christopher.

The eastern margin of the map cuts down the continent of Asia beyond the “Ganges,” so that the coastline is not shown. The most conspicuous feature in this quarter is the triangular island of “Trapobana.”

In latitude the map extends from the Scandinavian peninsula to the southern part of the African continent.

The African coast as far as the Cape of Good Hope is represented with fair accuracy, from Portuguese sources. The eastern coast, however, seems to be entirely imaginary.

In the Indian Sea, almost in the centre, are two large islands, “Zanabar” and “Madagascoa,” as on Behaim’s globe.

The sole indication of da Gama’s voyage is the inscription “Tierra descubierta por el Rey don Manuel de Portugal” on the south coast of Asia; the outline of the coast, however, is no improvement on that of the Catalan map of 1375.

The map in fact has every appearance of having been put together from at least two sections: the western portion — comprising the American discoveries and perhaps the West African coasts — having been joined to a portion of a world map resembling those of fifty years earlier which display the influence of Ptolemy.

If we use the distance between the tropic and the equator to obtain a scale of degrees and apply this to the map, we find that in the western section, though there are discrepancies, the general picture is not wildly inaccurate.

The newly discovered lands are placed in fair relationship to those of western Europe. The longitudinal difference between the Iberian coast and Hispaniola is apparently about 62°, instead of 59°, and between the African coast and the northeast coast of South America approximately 16°, instead of 17⅔°.

For a reason which has never been satisfactorily explained, Hispaniola and Cuba are placed well to the north of the tropic; the north coast of Cuba is shown at approximately 36° N., some 12° too far north.

Whatever the reason for this, it would appear that the Central and South American portion is on a larger scale than the rest of the map.

The representation of Africa is distorted by the excessive length of the Mediterranean.

The general shape of the western coastline is good, though, in relation to the west–east extent of the Gulf of Guinea coast, the coastline southwards to the Cape is too short.

This was a characteristic of early Portuguese charts of this region: owing to adverse sailing conditions, it was usual to underestimate distances run.

North-Eastern Coastline of America on La Cosa

Much attention has been attracted to the representation of the north‑eastern coastline of America.

The principal features are: (1) a prominent cape, “Cavo da Yngleterra,” about 1,300 miles from south‑west Ireland and approximately in the same latitude; (2) to the west of this cape, an extent of coastline running about due west for approximately 1,200 miles — a number of features along this coast are named, and this is the only portion of the North American coastline on which names occur; (3) beyond this coast, a stretch without names continues for another 700 miles, forms a bay, “Mar descubierta por Yngleses,” and then turns southwards.

The “Cavo da Yngleterra” is shown at about 56° N. latitude. Since, however, the latitudes of many places in Europe are out by several degrees (Land’s End, for example, is shown 4° too far north), the Cavo may be assumed to be not further north than 51°30′ N., which would put it in the neighbourhood of Belle Isle Strait.

On the other hand, the 1,200 miles of explored coastline is in all probability southern Newfoundland or Nova Scotia, so that the Cavo da Yngleterra must have lain further south, and Cape Race at once suggests itself, though this is no more than a possibility. J. A. Williamson, who credits this charting to the Cabots in 1497–98, believes that the Cavo was Cape Breton, while G. E. Nunn identifies it with Cape Farewell in Greenland.

The Cantino Chart

The earliest Portuguese example of these New World charts is the Cantino chart. It owes its name to the fact that it was procured for the Duke of Ferrara, Ercole d’Este, by one Alberto Cantino.

The Portuguese king had placed an embargo on the provision of charts showing the new discoveries, and Cantino obtained this clandestinely to satisfy the curiosity of the Duke, anxious at the threat to the Italian share in the spice trade.

As correspondence concerning the transaction has survived, we know that the chart was received by the Duke in November 1502 and that it embodied discoveries as late as the summer of that year.

The chart is clearly the work of a Portuguese cartographer; at a later period some amendment appears to have been made to the Brazilian portion, and half a dozen Italianized names were added.

The title given to it suggests that the main interest of the draughtsman was in the western discoveries: “Marine chart of the islands recently discovered in the parts of the Indies.”

The chart is large, so that the coasts are shown in considerable detail, and names are numerous.

The Equator and tropics are drawn in, but there is no graduated scale of latitudes. From west to east it extends from Cuba to the eastern coast of Asia.

The Tordesillas demarcation line between the Spanish and Portuguese spheres is inserted, and the Portuguese discoveries in the north‑west are made to lie just on the Portuguese side of the line.

The African continent is shown for the first time with something closely approaching its correct outline: on the east coast the names of Sofala, Mozambique, Kilwa, and Melinde occur, and the island of Madagascar is inserted but not named.

The Indian subcontinent is drawn as a sharply tapering triangle, on the western coast of which are names — e.g. Cambaya, Calecut — and legends detailing the wealth of these parts, drawn from accounts of Vasco da Gama’s voyage.

These appear to mark the limit of first‑hand knowledge; beyond, the outline must have been inserted largely by report.

That this was obtained from native seamen is probable from the circumstance that the term “pulgada” is used in place of a degree; it equalled about 1°42′50″.

The places whose latitudes are given thus are inserted only approximately in their correct positions. East of India is a large gulf and then a southward-stretching peninsula, a relic of the coasts which Ptolemy believed to enclose the Indian Ocean.

Near its extremity occurs the name “Malaqua,” and off it the large island of “Tl’aporbana” (Sumatra). The eastern coast of Asia runs away to the north‑east, almost featureless but with a number of names, mostly unidentifiable, on the coast and indications of shoals offshore. Recognizable names include “Bar Singapur” (Singapore) and “China cochin.”

The main feature to be noted with regard to Asia is the almost complete abandonment of Ptolemy’s conception of the southern coasts and the great reduction in the longitudinal extent of the continent.

The south‑eastern coastline of Asia is shown as lying approximately 160° east of the line of demarcation, a figure very close to the truth.

King‑Hamy Chart and Longitudinal Extent

The so‑called King‑Hamy chart, also dated 1502, is interesting as showing Ptolemaic conceptions of Asia in the process of being fitted to the new discoveries in the west.

This chart has many features of the Ptolemy world map in south‑east Asia, where “Malacha” and “Cattigara” appear together, but the point of importance is that the longitudinal extent eastwards from the demarcation line to the south‑east Asian coast is still approximately 220°–230°.

The Cantino chart therefore demonstrates clearly that Portuguese cosmographers had entirely abandoned the Alexandrian figures and were already aware that the Spanish discoveries in the west, far from neighboring on Cipangu and the Asian mainland, were separated from them by an interval of almost half the circumference of the globe.

The chart might be said to predict the existence of the Pacific Ocean.

The fact that the cartographer has a legend on the discoveries in the north‑east American shores stating that they were thought to be part of Asia does not controvert this.

For the Portuguese, theoretical and practical considerations happily coincided in this instance; when the question of sovereignty over the Moluccas arose, it was to their interest to reduce the longitudinal extent of Asia in order to bring the coveted islands within their sphere.

Canerio Chart and Waldseemüller

Another world chart, slightly later than the Cantino but derived from a very similar source, has also survived. This is a copy made by an Italian draughtsman, Nicolay de Canerio of Genoa, and assigned to the year 1505 or 1506 on the evidence of its portrayal of the Brazilian coast.

The interest of this chart lies in the fact that it is the basis of Waldseemüller’s wood‑cut world map of 1507. In general it is less accurate than the Cantino chart, particularly in its representation of Africa and India, although it places the Cape of Good Hope in the very accurate latitude of 34° S. (actual 34°22′ S.).

Off the mainland of north‑east Asia is an island “Chingirina” with the legend “This island is very rich, and they are Christians; thence comes the porcelain to Malacca. Here there is benzoin, aloes, and musk.” It has been suggested that this is a reference to Japan.

These world charts are evidence of the great interest taken in Italy in the Portuguese progress eastwards; had these copies not been demanded by Italian patrons, much valuable cartographic evidence would be lost to us.

They further show that much knowledge of the east had filtered through to the Portuguese before they reached Malacca.

Smaller Charts and Pedro Reinel

In addition to these world charts, there are from the first decade of the sixteenth century a few charts of smaller areas.

Three of these are of special interest: a chart of the North Atlantic, c. 1502, signed by Pedro Reinel; a chart of the North and South Atlantic, c. 1506 (generally referred to as Kunstmann III); and a chart of the Indian Ocean of about 1510.

The Pedro Reinel chart, the earliest signed work of a Portuguese cartographer, introduces the feature of the “oblique meridian.”

Off the land of Corte Real in the north‑west Atlantic is a scale of latitude, additional to the main scale, and placed obliquely to it.

H. Winter has shown that this is intended to indicate the geographical meridian in this area, and that the angle which it makes with the main meridian is the magnetic variation — in this instance 22° W.

Since the ordinary pilot would not be equipped to determine the variation, the coasts were laid down by the compass without correction, and the oblique meridian gave the allowance to be made when they were transferred to a graticule of latitude and and longitude.