The World of Gerard Mercator: The Mapmaker Who Revolutionised Geography. Andrew Taylor

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СКАЧАТЬ a matter of measurement and calculation rather than the simple telling of stories. Like Mercator some fourteen centuries after him, he designed and made instruments for measuring angles and altitudes in the heavens; his Geographia includes descriptions of a brass astrolabe and a quadrant for calculating the height of the Sun in the sky.

      Ptolemy knew the true location of a place could be fixed by taking precise sightings of the stars. The Geographia therefore included a catalog of some eight thousand place-names, rivers, mountains, and peninsulas, each of them with its position defined by degrees of latitude and longitude. It is a work of staggering ambition and exactitude – the first time anyone had attempted to use coordinates in such a precise way. Many of the observations Ptolemy needed to make the calculations had already been taken, but to place cities in remote or unexplored parts of the world, he had no choice but to rely on traditional accounts and the estimates of travelers. In such a case, he said, the mapmaker should use his judgment as to what figures to use, “deciding what is credible and what is incredible.”⁴

      It is impossible to know whether Ptolemy drew any maps to go with his Geographia. The illustrations that adorned medieval versions of his books were additions by later copyists working to his descriptions and coordinates, but in them his worldview, with the traditional three continents of Europe, Asia, and part of Africa, can clearly be recognized. Taprobane is grotesquely out of proportion in comparison with the half-formed India that lies to its north, and the coastline of the Far East is clearly drawn largely from imagination, but the Arabian peninsula and the whole of the Mediterranean basin are presented in some detail.

      Perhaps most important of all, though, Ptolemy left open the possibility that there were more lands to be discovered beyond the extent of his own knowledge. Where the Romans and Greeks who came before him had been content to keep their studies inside the limits of the habitable world, his interest was in the Earth as a whole, and geography, for him, was no more or less than the art of making maps. “It is the prerogative of Geography,” he said, “to show the known habitable earth as a unit in itself, how it is situated and what is its nature; and it deals with those features likely to be mentioned in a general description of the earth, such as larger towns and great cities, the mountain ranges and the principal rivers.”⁵

      The circle of seas that surrounded the Earth in the early T-O maps was one way of suggesting a round world, but Ptolemy’s was the first serious attempt to deal with the problem of projection. He described two possible solutions, based on a simple rectangular grid that ancient Greek philosophers had already devised, but adapting it to take account of the fact that the Earth was curved, not flat.* The systems he suggested were, as they had to be, a compromise, and one which worked satisfactorily enough within the limits of the known world. Even in the sixteenth century, most maps were still produced on grids that were simple adaptations of Ptolemy’s projections. Mercator’s greatest achievement would lie in rethinking these fifteen-hundred-year-old proposals.

      Ptolemy’s geographic writings are filled with errors of fact, many of them, as he engagingly admitted himself, due to a lack of basic information. Some, such as the “great southern continent” that he believed must balance the world on its axis, would endure, like the fabulous creatures described by Herodotus and other Greek writers, for centuries after Mercator.

      For all its shortcomings, though, the rediscovery and publication of the Geographia in the West laid the foundations for the work of the great cartographers of the sixteenth century. The book traveled with Columbus to the New World; when Mercator compiled his great world map of 1569, he began with Ptolemy’s calculation of the position of Alexandria. The Geographia was still being treated as the ultimate authority fourteen hundred years after its author’s death. It shows a man trying to apply scientific methods to achieve a precise, objective representation of the world in a way that was unique in his time, and remained so until Mercator’s day.

      IN THE EAST, the scanty records and remains of the work of the Chinese suggest that they had their own impressive tradition. Around the third century AD, a government minister of works named Phei Hsiu set out official principles for the making of maps under the Chin Dynasty. The most important of these was that they should be constructed on a rectangular grid in order to create a consistent scale and locate places accurately. There is no evidence that Ptolemy’s thinking had reached the Far East – a grid system had been introduced in China some two hundred years before Phei Hsiu by Ptolemy’s near-contemporary Chang Heng, an astronomer royal of the Han Dynasty.* He wrote of a spherical world suspended in infinity, like a yolk in an egg, and the system he introduced of building up a map by equal squares – “casting a net over the Earth,” in a contemporary phrase – was the basis of Chinese cartography for centuries.

      Chang Heng’s grid made no allowance for the curvature of the Earth, and it is hard to know from what is left of ancient Eastern cartography whether his image of a spherical world had any effect on current thought. There are no indications that early Chinese mapmakers realized the world was a sphere, that the lands they were mapping were consequently curved, nor whether the challenge, which still fascinates cartographers, of representing such a three-dimensional world on a flat surface had even occurred to them as a problem.

      In the Islamic world, Arab mapmakers drew on the ideas of Ptolemy and the Greeks to develop their own traditions. By the eighth century, they were compiling maps for overland diplomatic missions to China, military campaigns, and trading expeditions; the tales of Sindbad the Sailor, dating from some two hundred years earlier, are ample evidence of their seafaring traditions. Unlike the work produced by medieval monks in Europe, their maps seem to have been designed for use as much as for study, but they were still based mainly on copies of older European originals. There are early versions of the T-O maps, with south at the top and Mount Sinai in the center and, slightly later, more distinctively Arab interpretations in which a disk-shaped world, surrounded by water, is pierced from the east by the Arabian Gulf and the Red Sea, and from the west by the waters of the Mediterranean.

      Later mapmakers of the tenth and eleventh centuries were often slave dealers or traders, making their way north to the shores of the Caspian Sea and up the Volga River deep into the heart of Asia. Asian tribesmen, Russians, Norsemen, and Arabs would meet on one of the medieval world’s great trading routes, exchanging goods, knowledge, and ideas.

      One account, by the writer Ibn Haukal, author of The Book of Roads and Kingdoms, which contained a map of the Islamic world as it was then known, described a meeting toward the end of the tenth century with the great Arab cartographer al-Istakhri. “He showed me the geographical maps in his work, and, when I had commented on them, he gave me his work with the words, ‘I can see that you were born under a lucky star, therefore take my work and make such improvements as you think fit.’ I took it, altered it in several particulars, and returned it to him.”⁶

      There was cooperation not just between individuals but between cultures. One of the greatest of all the Arab cartographers, Muhammed al-Idrisi, was born in Morocco, studied at Cordoba in Islamic Spain, and worked at the twelfth-century court of the Christian king Roger of Sicily. There, he produced several world maps that drew directly both on Ptolemy and on the observations of Arab travelers, and which were still being used as models by Islamic cartographers four hundred years later. Among them were a large rectangular map in seventy sheets, and a smaller, circular map, similar to the T-O maps of the West, but incorporating curved parallels, which suggest that al-Idrisi was aware of the spherical shape of the world. The maps and sources that he used are lost, but the geographic detail he provided was far in advance of anything that was being produced by the copyists in Europe’s monasteries. Al-Idrisi’s representation of Spain, for example, with the northern coast of Africa, the Straits of Gibraltar, and Bay of Biscay all clearly discernible, is far more detailed than the stylized version presented around the same time by European mapmakers. When Al-Idrisi described Britain as “a great island, shaped like the head of an ostrich,” and the peninsula СКАЧАТЬ