I didn't know there was a #30DayMapChallenge. Thanks to @clhenrick for the heads-up. Here's a #map I #georeferenced for a friend the other night, who was curious how the 1909 'Map of #Ohlone #shellmounds in the #SanFranciscoBayArea from Nels C. Nelson's 1909 publication SHELLMOUNDS OF THE SAN FRANCISCO BAY REGION' would look, on a modern map. I know this isn't a new thing, others have done it, but here's my contribution in 72dpi, attached, and 600dpi, downloadable from here:
https://drive.google.com/file/d/1-gvzZ84uNxdleFz_pmm1iixgHQ3OEEDk/view?usp=drive_link
I used this file's largest available version, #QGIS and #OpenStreetMap to generate it:
https://commons.wikimedia.org/wiki/File:Shellmound_map.png
It is fascinating to see the coastline changes since 1909. The man-made portion of #TreasureIsland doesn't exist, and it's Goat Island. I can share the .qgz file, if you want it.
I've gone down the rabbit hole, reading about #shelllmounds. Many blog posts here:
https://fastestslowguy.blogspot.com/search/label/shellmound
And even more #NewspaperClippings here:
https://www.newspapers.com/clippings/?query=shellmound&user=3570264%3Amorganfletcher&tag=shellmounds