A-GPS or Assisted GPS is a system that relies on mobile data transmission (mobile internet) to help your mobile phone start GPS applications in record time. Without this system, finding available satellites could take up to 12 minutes.
Basically, the phone connects to a server that transmits the positions of the satellites at that time above the area where the mobile phone is. The location of the phone is found by triangulation using the approximate distances from the GSM mobile telephony antennas, the use of gps trackers can be helpful on daily activates like your job, meeting up with friends, etc. In this way the GPS application starts in a record time of only a few seconds.
A-GPS technology for mobile phones
The use of A-GPS also implies a consumption of mobile data for this exchange of information with the server that contains the positioning data of the satellites.
Find more interesting information here.