I’ve messed around with the Google wifi geo stuff before. It’s a little creepy. I don’t remember off the top of my head, but they somehow can pull the SSID of your wifi network and your MAC address (or the MAC address of your router–something along those lines) to make your SSID+MAC unique for future lookups. Failing the MAC address, they can look up the owner if you public IP using ARIN and use the SWIP’ed info to get your city. If your phone (or other computing device) has location services available from GPS/cell tower, they will store that data with your SSID.
At one point, they bought a company named Meraki (now owned by Cisco) who did easy-to-setup wifi mesh networking. When network admins placed the Meraki units on the map in their dashboard, Google would use that info to figure out your location using the Meraki dashboard data!
Even Apple uses Google to look up geoIP information from an iOS device. I discovered this while developing a canvassing iOS app. It took some snooping, but I discovered it would ping Google when the app did a geo lookup to get its location when on a wifi network. At one point, Google’s service went down for about 10-15 minutes, which is why I had to look it up in the first place!