Ptolemy's world map

The Ptolemy world map is a map of the world known to Greco-Roman societies in the 2nd century. It is based on the description contained in Ptolemy's book Geography, written c. 150. Based on an inscription in several of the earliest surviving manuscripts, it is traditionally credited to Agathodaemon of Alexandria.

Notable features of Ptolemy's map is the first use of longitudinal and latitudinal lines as well as specifying terrestrial locations by celestial observations. The Geography was translated from Greek into Arabic in the 9th century and played a role in the work of al-Khwārizmī before lapsing into obscurity. The idea of a global coordinate system revolutionized European geographical thought, however, and inspired more mathematical treatment of cartography.

Ptolemy's work probably originally came with maps, but none have been discovered. Instead, the present form of the map was reconstructed from Ptolemy's coordinates by Byzantine monks under the direction of Maximus Planudes shortly after 1295. It probably was not that of the original text, as it uses the less favored of the two alternate projections offered by Ptolemy.