On the precision of Ptolemy's geographic coordinates in his Geographike Hyphegesis

Abstract. In his Geographike Hyphegesis (~150 AD) Claudius Ptolemy catalogued the positions of over 6300 ancient locations in the form of geographic longitude and latitude. A determination of the frequencies of the fractions of the degrees indicates that the coordinates are given with different precision/resolution and larger regional differences. The author's assumptions concerning the origin of the detected form of the frequency distribution were examined with statistical hypothesis tests and partly confirmed. Differences between the frequencies of the Ω- and Ξ-recension were investigated in terms of possible transcription errors in the manuscripts. A calculation method is given with which the properties of coordinates of different resolutions can be estimated. It is applied both globally and regionally. Such basic information about the precision of the Ptolemaic coordinates is important for detecting systematic and gross errors in the Ptolemaic coordinates and thereby for the identification of the Ptolemaic locations with their today's place.