Based on the data given in Claudius Ptolemy’s Geography (2nd century CE), which contains information on more than 6,000 localities distributed over the then known world, the project investigated the genesis and transformation of geographical information in Antiquity. The aim was to gain insight into the methods used by ancient scientific geographers to systematize individual space data.


A first study for the area of the map of Asia Minor has shown, among other things, that geometric methods played a crucial role in the genesis of the values of the Geography: Ptolemy used constructions employing ruler and compass to plot the positions of individual places on the basis of documented distances. Major sources for these constructions – besides the records of latitudes attributed to Hipparchus – are records for distances between cities at the coastline which also have been transmitted to us through Strabo’s geographical writings. Using the same research methods, Ptolemy’s map of the Iberian Peninsula has been investigated. The project confirmed many of the previous results, especially the fact that Ptolemy used geometrical processes, built progressively his map and established afterwards his list of localities.

Moreover, Ptolemy’s personal working method and the Geography’s textual transmission history are inseparable research themes. Indeed, major uncertainties still surround its original text, because of the existence of two different versions of the Geography (known as the Ξ and the Ω recensions). Although much information on the history of Ptolemy’s text can be gleaned from philological and codicological studies, it is harder to detect deliberate changes to the coordinates using traditional philological investigations. Understanding Ptolemy’s working method can help us shed light on the transmission of Ptolemy’s coordinates and find the answers to certain questions that would otherwise remain unsolved. The study shows that the order of the inland localities in the catalogue, which was based on a strict spatial principle explained in the introduction of Ptolemy’s work, indicates that the coordinates in the Ω recension underwent important modifications, intentional or otherwise. Therefore, it seems more likely that the set of coordinates supplied by the Ξ recension is closer, in the majority of cases, to Ptolemy’s original work than the coordinates provided by the Ω recension. Other elements suggest that the existence of two versions of the Geography should not be regarded as the division of the tradition into two recensions but as the separation of the Ω recension from the main tradition. Widening the scope of the philological investigation so that it covers the links between the catalogue and the maps enables us to define the Geography’s context of production as well as a more precise approach of Ptolemy’s geographical and cartographical methods.

Further information on the topic can be found in: Gerd Graßhoff, Elisabeth Rinner, Mathieu Ossendrijver, Olivier Defaux, Marvin Schreiber and Emilie Villey, “Longitude”, in: Space and Knowledge. Topoi Research Group Articles, eTopoi. Journal for Ancient Studies, Special Volume 6 (2016), 634–677