Page "Ptolemy" Paragraph 17

Maps based on scientific principles had been made since the time of Eratosthenes ( 3rd century BC ), but Ptolemy improved projections.

It is known that a world map based on the Geographia was on display in Augustodunum, Gaul in late Roman times.

In the 15th century Ptolemy's Geographia began to be printed with engraved maps ; the earliest printed edition with engraved maps was produced in Bologna in 1477, followed quickly by a Roman edition in 1478 ( Campbell, 1987 ).

An edition printed at Ulm in 1482, including woodcut maps, was the first one printed north of the Alps.

The maps look distorted as compared to modern maps, because Ptolemy's data were inaccurate.

One reason is that Ptolemy estimated the size of the Earth as too small: while Eratosthenes found 700 stadia for a great circle degree on the globe, in the Geographia Ptolemy uses 500 stadia.

It is highly probable that these were the same stadion since Ptolemy switched from the former scale to the latter between the Syntaxis and the Geographia, and severely readjusted longitude degrees accordingly.

If they both used the Attic stadion of about 185 meters, then the older estimate is 1 / 6 too large, and Ptolemy's value is 1 / 6 too small, a difference explained as due to ancient scientists ' use of simple methods of measuring the earth, which were corrupted either high or low by a factor of 5 / 6, due to air's bending of horizontal light rays by 1 / 6 of the Earth's curvature.

See also Ancient Greek units of measurement and History of geodesy.