Excerpt:
Claudius Ptolemy was an astronomer and mathematician of the 2c A.D., whose exact dates we do not know, but who must apparently have worked in Alexandria between A.D. 127 and 148 since some of his astronomical observations are consistent with those dates.
(Thus the Oxford Classical Dictionary. The Geography itself also provides at least one clue, listing the Egyptian city of Antinoöpolis, founded in A.D. 130.)
Annotation:
This site is an interesting project that attempts to recreate Ptolemy's maps of various locations in Europe. Though the maps were not recopied (images were more difficult for monks to transcribe than words), the index indicates that the original work included maps. In an effort to recreate these maps, Professor Thayer has used orginal coordinates. The level of detail is remarkable as map images include clickable place names - the anchored link taking the viewer to the longitudinal and latitudinal coordinates. The site includes a brief introduction to Ptolemy and his "Geography" as well as links to other sites about Ptolemy.