Re-mapping Ptolemy

http://penelope.uchicago.edu/Thayer/E/Gazetteer/Periods/Roman/_Texts/Ptolemy/home.html

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.)

Ptolemy's most famous works are the Almagest, a 13‑book textbook of astronomy in which among many other things, he lays the foundations of modern trigonometry; the Tetrabiblos, a compendium of astrology; and the Geography. He also wrote many other works centered on applied mathematics: astronomy, optics, music, etc.; a small Canon of Latitudes and Longitudes may be his as well: it is a sort of abridged version of the Geography, although the coördinates for certain places are not the same — manuscript transmission problems, maybe.

Ptolemy's coördinates are in degrees and minutes (360 degrees to a circle, 60 minutes to a degree), just like our own. His North-South coördinates (latitudes) are measured like our own from the Equator. His East-West coördinates (longitudes) are measured eastward from a point somewhere W of the westernmost point he catalogues in the Geography, traditionally read as "east of the Blessed Isles": for that reason, in this Web edition I indicated latitudes with the familiar degree sign (e.g., 5°00N), but his longitudes with an asterisk instead (e.g., 25*00).

Ptolemy's Geography was what we would now call an atlas, the core of which were of course the maps, referred to in the text and table of contents below as "Fifth Map of Europe", "Third Map of Asia", etc. The manual copying of maps is fiendish work, however, and considerably less reliable than that of text — Ptolemy was well aware of this (Book I, Chapter 18) — and his maps have consequently disappeared: nothing remains but the index. Recognizing that the maps would be a sticking point, Ptolemy also suggested that people replot his data, and a good section of Book I of the Geography offers advice on how to draw the maps.

Various people at various times have redrawn the maps from the coördinates given in the work: the map appended to Prof. Stevenson's edition, for example, is a medieval version or copy of just such a replot, but both Planudes and Karl Müller have done it as well. Thus, in undertaking this Web edition at the end of the 20th century and the beginning of the 21st, I found myself very moved to be, and in good company at that, following Claudius Ptolemy's instructions using instruments he would never have dreamt of: every once in a while, this would hit me for a few seconds and make the unspeakably tedious cartographic reproduction much easier.