Originally Posted by
BertieBadger
Typo for GPS I assume, GSM being the cellular signal?
Virtually all cell phones use something called A-GPS (
https://en.wikipedia.org/wiki/Assisted_GPS) that uses cell tower signals to find your first position. The initial accuracy doesn't need to be that high, it's just trying to reduce the time and power it takes to lock on to satellites.
If you're on recent Android releases, the way they find your position is a blend of a bunch of different things, not just GPS. If you want _serious_ detail, Google puts out an Android developer podcast, and there was a recent show on location providers.
Android Developers Backstage: Episode 96: Location: It's Where It's At