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This envelope used to be a map
(feddit.org)
This is for strictly mildly interesting material. If it's too interesting, it doesn't belong. If it's not interesting, it doesn't belong.
This is obviously an objective criteria, so the mods are always right. Or maybe mildly right? Ahh.. what do we know?
Just post some stuff and don't spam.
I resolved the ISBN printed on the reverse side. Took some trial and error (some 30 possible options unless you can read barely-visible EAN barcodes by sight) but there is a check digit so I didn't have to search online for every combination.
https://www.isbn.de/buch/9783832610234/l2546
Nope, it's a regular topographic map you can buy for €8 or $10. They're published by a government body and the data is freely available online, which you can use much like the OSM database.
You went above and beyond!