Ptolemy's World Map and Eratosthenes's Circumference of the Earth

摘要

The interlink between the determination of the circumference of the Earth and the geographical mapping performed by Ptolemy in his Geography is discussed. It is shown that a simple transformation of the Ptolemaic coordinates to the (bigger) circumference of the Earth measured by Eratosthenes drastically improves the positions of the locations given in Ptolemy's catalogue. As a consequence, by linking the recalculated positions of the identified localities with their actual positions, the very high precision of Eratosthenes' result for the circumference of the Earth is confirmed.