Anyone knows if there is a free geoip lookup database with city level detail? If not, if there was a way of crowdsourcing this somehow? If I'm not mistaken gps+phone probably wouldn't work since the IP addresses seem to be more or less random.

Google seems to know wifi routers locations, but afaik they use their streetcar fleet to create it. It was funny sometime ago that after moving cities but keeping the same wifi router, my detected location was still at the old place. Eventually it got corrected.

It would be possible with a different map and some changes to make this go to city level, I might do that some time in the future but I don't know how much extra work would be required and I assume it would require a whole lot more processing.