GPS and AGPS
AGPS uses the same global satellite system as GPS to compute your location, thus achieving the same level of performance in terms of accuracy (and sometimes better).
Its principle is to provide the device with a number of additional information that a usual GPS receiver has to demodulate from the CDMA signal from the satellites, which can take a long time, particularly indoors or under an athermic windshield. The data provided can include timing information, satellites ephemeris, signal correction parameters, and an estimated initial guess for your location. With all that a cold start only takes a few seconds, as opposed to a few minutes with regular GPS.
@Greg : the 1700m fix you get is only the initial cell-ID location, it is not the final (A)GPS position (leave it some time). If AGPS does not work at least as well as GPS for you, have a pro configure your phone.
Biting the hand that feeds IT
