The g tag for nostr events supports putting a geohash or other geojson data into an event. I would take events with this data and visualize them on Open Street Maps, probably via MapBox or something like that.
Discussion
I would like to build something in that direction, but I see too many unsolved questions to just start bootstrapping. Your notes definitely inspired me to do more research on map data formats, editing and rendering today.
Instead of just maps we should have a Nostr based cadastre.
And instead of only Nostr, it should tie into a universal identity system like what #[3] works on with https://pkarr.nuh.dev .
pkarr is awesome! Thank you for sharing