Global Positioning System, or GPS, works through cell phone towers and satellites.
The government currently has 24 satellites that track GPS. Your device locks onto these satellites. Only 3 satellites are needed to triangulate and pinpoint your location. With 6-10 satellites, your location is as accurate as 15-30 feet of your vehicle. The more satellites available, the more accurate your results!
The data obtained from these satellites is then sent directly to the device and stored there. As you near cellular towers, the data is then relayed through them using the same technology as your mobile device!
The information is then loaded through a data processing system, which is accessible to you through the internet. Since this is entirely internet based, you have access to this information anywhere you have internet access!