Hey violent,
Check this out:
http://en.wikipedia.org/wiki/Gps
Basically, GPS works using satellites, cellular works using towers. As far as I know, there is no such thing as a GPS tower.
To expand on that, Assisted GPS (aGPS) works by using the cellular data connection on a mobile phone to assist the on-board GPS hardware in getting faster satellite locks.
So if you're in the middle of nowhere and don't have your cellular data connection available, you should still be able to get a GPS lock, as long as you have a clear view of the sky. It just may take a little longer because you won't have aGPS to help you get a quicker lock.
Hope that helps!
Myke...