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Hist. Geo Space. Sci., 9, 9-24, 2018
https://doi.org/10.5194/hgss-9-9-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
 
01 Feb 2018
The length of coastlines in Ptolemy's Geography and in ancient periploi
Dmitry A. Shcheglov S.I. Vavilov Institute for the History of Science and Technology, St. Petersburg, Russian Federation
Abstract. The lengths of the coastlines in Ptolemy's Geography are compared with the corresponding values transmitted by other ancient sources, presumably based on some lost periploi (literally "voyages around or circumnavigations", a genre of ancient geographical literature describing coastal itineraries). The comparison reveals a remarkable agreement between them, suggesting that Ptolemy relied much more heavily on these or similar periploi than it used to be thought. Additionally, a possible impact of Ptolemy's erroneous estimate of the circumference of the Earth is investigated. It is argued that this error resulted in two interrelated distortions of the coastal outlines in Ptolemy's Geography. First, the north–south stretches of the coast that were tied to particular latitudes are shown compressed relative to the distances recorded in other sources in roughly the same proportion to which Ptolemy's circumference of the Earth is underestimated relative to the true value. Second, in several cases this compression is compensated by a proportional stretching of the adjacent east–west coastal segments. In particular, these findings suggest a simple explanation for the strange shape of the Caspian Sea in Ptolemy's Geography.

Citation: Shcheglov, D. A.: The length of coastlines in Ptolemy's Geography and in ancient periploi, Hist. Geo Space. Sci., 9, 9-24, https://doi.org/10.5194/hgss-9-9-2018, 2018.
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The lengths of the coastlines in Ptolemy's Geography are compared with the corresponding values transmitted by other ancient sources, presumably based on some lost periploi (literally "circumnavigations", a genre of ancient geographical literature describing coastal itineraries). The comparison reveals a remarkable agreement between them, suggesting that Ptolemy relied much more heavily on these or similar periploi than it used to be thought.
The lengths of the coastlines in Ptolemy's Geography are compared with the corresponding values...
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