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Spent 3 hours trying to geo-locate a 1730s map of the Adriatic and the coastline didn't match anything
Pulled up a scanned portolan chart from a Naples archive and the whole eastern shore was drawn about 40 miles too far north, which had me second-guessing my overlay for hours. Turned out the cartographer was working from a bad Ptolemy translation, so the error was baked in from the start. Anyone got a go-to source for sorting out which old charts used Ptolemaic vs. dead-reckoning data?
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the_nathan6h ago
The "bad Ptolemy translation" thing got me down a rabbit hole last year. I always figured those old portolan charts were mostly dead reckoning and pretty solid for coastlines, but then I looked at the Catalan Atlas and realized a ton of them just copied Ptolemy's inflated Asia and messed up the longitude spacing. Now I check the chart's lineage first, like whether it traces back to Ptolemy or to actual sailing logs, before I even try overlaying it. The Ptolemaic ones drift way north the further east you go, which sounds like exactly what bit you.
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