Since October 2010 Elisabeth Rinner has been a research assistant at the Humboldt-Universität zu Berlin. Besides her teaching activities, she is working on the history of geography and cartography in antiquity, especially on the Geographike hyphegesis of K. Ptolemy. Comparing the Ptolemaic locations of places with their modern values makes it possible to find characteristic differences between both datasets, which result from the process of the genesis of Ptolemy´s geographic coordinates. This opens up a new way to identify methods and sources Ptolemy used to generate the values for longitude and latitude for the set of more than 6000 places given in his Geography.