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.

中文翻译：

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托勒密<i>地理</ i>和古代​​<i> periploi </ i>的海岸线长度

摘要。托勒密地理中海岸线的长度与其他古代资料所传递的相应值进行了比较，大概是基于一些遗失的围岩（字面意思是“环游或环游”，一种描述沿海路线的古代地理文献）。通过比较可以看出，托勒密之间存在显着的一致性，这表明托勒密对这些或类似的骨膜的依赖性大大超过了以前的想象。另外，研究了托勒密对地球周长的错误估计的可能影响。有人认为，这一错误导致托勒密《地理》中沿海轮廓的两个相互关联的变形。第一，与特定纬度相关的海岸的南北延伸显示为相对于其他来源记录的距离压缩，相对于托勒密的地球周长相对于真实值低估的比例大致相同。其次，在某些情况下，这种压缩可以通过相邻东西方沿海部分的比例拉伸来补偿。这些发现尤其为托勒密《地理》中关于里海奇特形状的简单解释。