The Practical Prognosticator - On the Use and Abuse of Ptolemy’s Geography

Posted on 31 January 2013

Talk: Dr. Leif Isaksen (University of Southampton, UK) "The Practical Prognosticator - On the Use and Abuse of Ptolemy’s Geography".


Date: Tuesday, 05 February 2013

Time: 17:00-18:30

Venue: TOPOI-Haus Dahlem, Hittorfstr. 18, 14195 Berlin (map).

Poster: Download the PDF here.


This paper will argue that Ptolemy’s Geography does not represent a linear development of Greek geographic thought but is instead a unique fusion of pre-Ptolemaic sources designed for a specific task that also conceals a compilation of both geographic and chorographic maps.

Part One will show that the Almagest, the Geography, and the Handy Tables all unequivocally state that the Geography’s function is to provide a terrestrial counterpart to the astronomical data compiled in the Almagest. This is expressly to derive local celestial phenomena for a given time in order to draw a wide range of astrological, meteorological and environmental conclusions. There is no evidence that it was intended to serve any other practical function.

Part Two will demonstrate that Ptolemy’s sources are ill-suited to this role. Geographic maps – representing the world as a whole - provided information vital for calculating relative time from his observational point at Alexandria and the relationship of locations to celestial bodies, but their reduced scale requires extremely limited coverage of individual locations. In contrast, chorographic maps- which represent individual regions - display dense relative configurations of cities but their relationship to the earth as a whole is left unclear. Unable to find satisfactory material for his stated purpose, Ptolemy is therefore obliged to create a new kind of map, using geographic sources (especially Marinos) as a global framework to which multiple chorographic sources can be pegged.

Part Three will use a variety of digital methods to expose the ways in which this combination of this fragmentary source material has left traces within the structure of the catalogue. These include toponymic comparisons, linear interpolation and Exploring these spatial and categorical ‘fractures’ opens up new possibilities for appraising ancient cartographic practice. It will also show how this change in perspective may even allow us to identify development and change within the sources themselves.


Or you can download the slides from here.