By the way, the nice OSM map is provided by https://www.mapbox.com/
Do you pull OSM data from somewhere to generate the map? I get the idea that the map is maybe being built from the shown imagery tiles, in which case OSM wouldn't be involved at all.
But, I agree. I've often thought how cool it would be to be able to generate game maps (for all sorts of games) of various real places, including places I'm familiar with. Civ is the low-hanging fruit. Not to say this isn't an impressive feat; it's very cool.
Edit: I've never played Freeciv before