another source of location data is cell phone towers (assuming you have a device that can see these). There is an open database of these http://realtimeblog.free.fr/ that could be used.
compared to GPS it has almost instant fix (GPS will usually take 30-60 seconds, but can be much longer from cold), highest resolution in cities (more towers) where GPS can have trouble due to less visible sky. however it is lower resolution, and needs a database or network connection. it can be used to seed a GPS for a quicker fix.