The Accuracy of Ancient Cartography Reassessed: The Longitude Error in Ptolemy’s Map

This essay seeks to explain the most glaring error in Ptolemy’s geography: the greatly exaggerated longitudinal extent of the known world as shown on his map. The main focus is on a recent hypothesis that attributes all responsibility for this error to Ptolemy’s adoption of the wrong value for the c...

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Bibliographic Details
Published inIsis Vol. 107; no. 4; p. 687
Main Author Shcheglov, Dimitry A
Format Journal Article
LanguageEnglish
Published United States 01.12.2016
Subjects
Astronomy - history
Dissent and Disputes - history
Earth (Planet)
Geography - history
Geology - history
History, Ancient
Humans
Mathematical Concepts
Weights and Measures - history
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Summary:This essay seeks to explain the most glaring error in Ptolemy’s geography: the greatly exaggerated longitudinal extent of the known world as shown on his map. The main focus is on a recent hypothesis that attributes all responsibility for this error to Ptolemy’s adoption of the wrong value for the circumference of the Earth. This explanation has challenging implications for our understanding of ancient geography: it presupposes that before Ptolemy there had been a tradition of high-accuracy geodesy and cartography based on Eratosthenes’ measurement of the Earth. The essay argues that this hypothesis does not stand up to scrutiny. The story proves to be much more complex than can be accounted for by a single-factor explanation. A more careful analysis of the evidence allows us to assess the individual contribution to Ptolemy’s error made by each character in this story: Eratosthenes, Ptolemy, ancient surveyors, and others. As a result, a more balanced and well-founded assessment is offered: Ptolemy’s reputation is rehabilitated in part, and the delusion of high-accuracy ancient cartography is dispelled.
ISSN:0021-1753
DOI:10.1086/689763