The irony of the Ptolemaic renaissance: geographical knowledge versus cartographical method, 1582

In the very years in which printing with movable type was being (re-)invented in the West, the maps described by Ptolemy were then refined by another monk, the German Benedictine Nicolaus Germanus (fl. 1451-1456). Within a coiuple of decades, they were also appearing in editions the Geographia such as that printed by Leinhart Holle in Ulm edition in1482 (Image 1). The appearance of these works just one decade before Columbus’s first voyage to the ‘New World’ unknown to the ancients exemplified the irony of this development: Ptolemy's fundamental cartographic principles were put in circulation at almost precisely the moment that his geographic knowledge began rapidly to be rendered obsolete.

Geographical knowledge. The most obvious defect of the map, to modern eyes, is that it is incomplete. Famously, ancient geographers were only aware of the continents which radiated out from the Mediterranean in three directions: Europe to the north, Asia to the east, and Africa to the south. Missing entirely from this map was the ‘New World’ of North and South America, which only emerged into European consciousness in 1492 (not to mention Australia and Antarctica, only ‘discovered’ by Europeans in 1606 and 1820 respectively). Less famous is a second defect strikingly evident in this map: for unknown reasons, Ptolemy depicted the Indian Ocean as a land-locked lake, surround by land much as the Mediterranean was (Image 2). 

The manner in which these defects were corrected is of profound consequence for assessing the contributions of humanist scholarship and artisanal observation to inaugurating aspects of the modern world. The most dramatic defects of this aspect of the received world view were corrected, not by erudite humanist scholars pouring over ancient manuscripts to recover lost learning, but by semi-educated mariners returning – from Columbus’s first trans-Atlantic voyage in 1493 and Vasco da Gama’s pioneering circumnavigation of the Cape of Good Hope in 1499 – to report what they had witnessed with their own eyes (Image 3). These momentous epistemological implications were lost neither on the artists who compiled the Nova Reperta or such architects of modern thought as Francis Bacon. 

Cartographical methods. Yet a countervailing appraisal is also in order. One of the most striking aspects of Ptolemy’s ‘world map’ is that it did not claim to be complete. On the contrary, it was deliberately restricted to that part of the world for which he had some kind of quantitative data. To the north, south, and east, the landmass depicted overflows the boundaries of the map, indicating the existence of wholly unknown regions. Moreover, the projection itself is confined to less than one quarter of the globe: namely the northern half of the eastern hemisphere, 80 degrees of latitude high and 180 degrees of longitude wide. This is one of the characteristics which most strikingly distinguished Ptolemy’s from the Medieval ‘mappa mundi’ tradition, which attempted to map the entire world in a symbolic and speculative fashion.

This distinguishing characteristic is rooted in an second and even more fundamental one: Ptolemy’s map was not symbolic or speculative but mathematical. The gazetteer which made up the vast bulk of Ptolemy’s text provided geographical coordinates (latitude and longitude) pinpointing around 8,000 individual places. The final section section of his book then outlined three different methods of increasing sophistication with which lines of latitude and longitude could be projected from a three-dimensional sphere onto a two-dimensional surface to provide the mathematical framework for a map. The most popular of these three alternatives was the second one (illustrated in Image 1 and 4), in which both the parallels of longitude (which wrap around the globe from east to west) and the meridians of latitude (which run north and south between the poles) are both curved: this arrangement allows the two-dimensional map to convey some impression of the sphericity of the earth. (The simpler and less effective first method is illustrated by the previous image).

Commentary. Howard Hotson (January 2024)