Doesn’t matter. As long as a single smartphone with GPS enabled roams past your WiFi (and sees its advertised MAC address), any app on the phone can associate the user’s GPS coordinates with your router’s MAC address. Do this with enough users, and enough routers, and you’ve got a nearly perfect geographical mapping of WiFi routers.

This isn’t a conspiracy; Apple and Google have been doing this sort of triangulation for a long time, and even use it as a method of saving battery while avoiding the GPS radio.

Any app on your phone, including the Facebook app, can see nearby WiFi networks (maybe this is a gated permission now?). If the app has enough users with GPS enabled, its developer can easily build a GPS/WiFi map.