Editing Ptolemy (section)

===''Geography''===
{{Main|Geography (Ptolemy)}}
{{further|Ptolemy's world map}}
[[File:Claudius Ptolemy- The World.jpg|thumb|upright=1.1|A printed map from the 15th century depicting Ptolemy's description of the ''[[Ecumene]]'' by Johannes Schnitzer (1482).]]
Ptolemy's second most well-known work is his ''Geographike Hyphegesis'' ({{Langx|el|Γεωγραφικὴ Ὑφήγησις}}; {{Lit|Guide to Drawing the Earth}}), known as the ''[[Geography (Ptolemy)|Geography]]'', a handbook on how to draw maps using [[geographical coordinates]] for parts of the [[Roman Empire|Roman world]] known at the time.<ref name="Graßhf-Mittnhbr-Rinner-2017">
{{cite journal
 |last1=Graßhoff |first1=G.
 |last2=Mittenhuber |first2=F.
 |last3=Rinner |first3=E.
 |year=2017
 |title=Of paths and places: The origin of Ptolemy's ''Geography''
 |journal=[[Archive for History of Exact Sciences]]
 |volume=71 |issue=6 |pages=483–508
 |doi=10.1007/s00407-017-0194-7
 |jstor=45211928 |s2cid=133641503
 |issn=0003-9519
}}
</ref><ref name=Isaksen-2011>
{{cite journal
 |last=Isaksen |first=L.
 |year=2011 |title=Lines, damned lines and statistics: Unearthing structure in Ptolemy's ''Geographia''
 |journal=E-Perimetron
 |volume=6 |issue=4 |pages=254–260
 |url=http://www.e-perimetron.org/Vol_6_4/Isaksen.pdf
}}
</ref>
He relied on previous work by an earlier geographer, [[Marinos of Tyre|Marinus of Tyre]], as well as on [[gazetteer]]s of the Roman and ancient [[History of Iran|Persian Empire]].<ref name=Isaksen-2011/><ref name="Graßhf-Mittnhbr-Rinner-2017"/> He also acknowledged ancient astronomer [[Hipparchus]] for having provided the elevation of the [[celestial pole#Finding the north celestial pole|north celestial pole]]<ref>The north celestial pole is the point in the sky lying at the common centre of the circles which the stars appear to people in the northern hemisphere to trace out during the course of a [[sidereal time|sidereal day]].</ref> for a few cities. Although [[maps]] based on scientific principles had been made since the time of [[Eratosthenes]] ({{Circa|276|195 BC}}), Ptolemy improved on [[map projection]]s.

The first part of the ''Geography'' is a discussion of the data and of the methods he used. Ptolemy notes the supremacy of astronomical data over land measurements or travelers' reports, though he possessed these data for only a handful of places. Ptolemy's real innovation, however, occurs in the second part of the book, where he provides a catalogue of 8,000 localities he collected from Marinus and others, the biggest such database from antiquity.<ref name=Mittnhbr-2010>
{{cite book
 |last=Mittenhuber |first=F.
 |year=2010
 |section=The tradition of texts and maps in Ptolemy's ''Geography''
 |title=Ptolemy in Perspective: Use and criticism of his work from antiquity to the nineteenth century
 |series=Archimedes
 |volume=23 |pages=95–119
 |place=Dordrecht, NL
 |publisher=Springer Netherlands
 |doi=10.1007/978-90-481-2788-7_4
 |isbn=978-90-481-2788-7
}}
</ref>
About {{gaps|6|300}} of these places and geographic features have assigned [[coordinate]]s so that they can be placed in a [[Grid (spatial index)|grid]] that spanned the globe.<ref name=Jones-2020/> [[Latitude]] was measured from the [[equator]], as it is today, but Ptolemy preferred to express it as ''[[clime|climata]]'', the length of the longest day rather than [[degree (angle)|degrees of arc]]: The length of the [[midsummer]] day increases from 12h to 24h as one goes from the equator to the [[polar circle]].<ref>
{{cite report
 |last=Shcheglov |first=D.A.
 |date=2002–2007
 |url=https://nw.academia.edu/DmitryShcheglov/Papers/142876/Hipparchus_Table_of_Climata_and_Ptolemys_Geography
 |title=Hipparchus' table of climata and Ptolemy's ''Geography''
 |series=Orbis Terrarum |volume=9 (2003–2007)
 |pages=177–180
}}
</ref>
One of the places Ptolemy noted specific coordinates for was the now-lost [[Stone Tower (Ptolemy)|stone tower]] which marked the midpoint on the ancient [[Silk Road]], and which scholars have been trying to locate ever since.<ref>
{{cite book
 |last=Dean |first=Riaz
 |year=2022
 |title=The Stone Tower: Ptolemy, the silk road, and a 2,000&nbsp;year-old riddle
 |publisher=Penguin Viking
 |isbn=978-0670093625
 |location=Delhi, IN
 |pages={{mvar|xi}}, 135, 148, 160
}}
</ref>

In the third part of the ''Geography'', Ptolemy gives instructions on how to create maps both of the whole inhabited world (''[[oikoumenē]]'') and of the Roman provinces, including the necessary [[Topographic map|topographic]] lists, and captions for the maps. His ''oikoumenē'' spanned 180&nbsp;degrees of longitude from the Blessed Islands in the [[Atlantic Ocean]] to the middle of [[China]], and about 80 degrees of latitude from [[Shetland]] to anti-Meroe (east coast of [[Africa]]); Ptolemy was well aware that he knew about only a quarter of the globe, and an erroneous extension of China southward suggests his sources did not reach all the way to the Pacific Ocean.<ref name="Graßhf-Mittnhbr-Rinner-2017"/><ref name=Isaksen-2011/>

It seems likely that the topographical tables in the second part of the work (Books&nbsp;2–7) are cumulative texts, which were altered as new knowledge became available in the centuries after Ptolemy.{{sfn|Bagrow|1945}} This means that information contained in different parts of the ''Geography'' is likely to be of different dates, in addition to containing many scribal errors. However, although the regional and [[Ptolemy's world map|world maps]] in surviving manuscripts date from {{Circa|1300&nbsp;AD}} (after the text was rediscovered by [[Maximus Planudes]]), there are some scholars who think that such maps go back to Ptolemy himself.<ref name=Mittnhbr-2010/>