Ptolemy's "Geography": An Annotated Translation of the Theoretical Chapters (review)

Ptolemy's "Geography": An Annotated Translation of the Theoretical Chapters. By J. Lennart Berggren and Alexander Jones. Princeton, N.J.: Princeton University Press, 2000. Pp. xii+192. $39.50.

The only complete English translation of Ptolemy's Geography is that by Edward Luther Stevenson, published by the New York Public Library in 1932. An expensive edition, limited to 250 copies, it was long out of print until reissued as a Dover paperback in 1991. Two generations of English-speaking readers thus know the Geography only through Stevenson's translation, which is very flawed. The most recent scholarly treatment in English of Ptolemy's cartography is a chapter by Oswald A. W. Dilke in volume 1 of the History of Cartography edited by J. B. Harley and David Woodward (1987). Aware of the inadequacy of Stevenson's translation, Dilke relied on modern Greek editions and provided new English translations of quoted passages. So it is very good, indeed, to have access at last to a reliable English-language version of the principal textual parts of Ptolemy's epochal work.

As the subtitle indicates, J. Lennart Berggren and Alexander Jones limit their new translation to the more theoretical chapters of the Geography. The most crucial data are the tables giving latitude and longitude for some eight thousand place-names in the Greek oikoumene. Stevenson included these, but they must be used very cautiously, as Berggren and Jones point out that even "the most conscientious scribe was certain to introduce numerous errors in copying its interminable lists" (p. 5). When it comes to the tables, they mistrust all the manuscripts and scholarly editions, and include only a small portion dealing with France as a way to give the flavor of the presentation.

Ptolemy's theoretical discussion begins with the distinction between world and regional cartography. Scale is obviously central, but he also argues that world cartography is more concerned with quantities, and hence dependent on mathematics, while regional (what we would call large-scale) cartography is concerned with qualities and "has no need of mathematical method" (p. 58). He next discusses the two basic ways in which places can be mathematically fixed for making a world map. The first is to have them astronomically located—that is, with latitudes determined from measurement of the height of the sun or pole star, and longitudes determined by comparing differences in local times of eclipses. Only a handful of locations available to Ptolemy would have met such a rigorous test. The second method is "surveying . . . through measurement of distance" (p. 59), which, for the large distances of a world map, could only mean the reports of travelers.

Almost invariably, travelers were careless, or they were not mathematically trained, or they were more interested in trade, and so their reports of the distances and directions between places were likely to be crude. Berggren and Jones summarize Ptolemy's plight by describing his data as forming "a loose framework of determined parallels and meridians between which one had to fit the otherwise hopelessly flexible strings of place names found in the other sources" (p. 28). Nevertheless, these crude data were often the best available, and, good scientist that he was, Ptolemy took great pains to explain how to edit and rectify this disparate material to make the best possible map.

First, the cartographer must always give precedence to data determined astronomically. He should prefer the most recent data. He should reduce reported road distances by a factor of one-half (to account for changes in direction and detours), and reduce reported sea distances by one-third (to account for irregular courses and variable speeds). Ptolemy applies such corrections to a number of locations and distances reported by Marinos of Tyre, a near-contemporary whose map and writings are known to us only through Ptolemy's comments on them. Ptolemy apparently used a great deal of the material Marinos had gathered, but subjected...