GPS (Global Positioning System) technology uses information from earth-orbiting satellites to find locations. A receiver estimates the distance to GPS satellites based on the time it takes for signals to reach it, then uses that information to identify its location. But the A-GPS (Assisted GPS) solution on iPhone 3G goes a step further, using a unique approach to find the closest satellites and more quickly identify your position. That gives you a faster fix on your location than with regular GPS.
Get the signal.
In addition to A-GPS, iPhone 3G uses signals from GPS satellites, Wi-Fi hot spots, and cellular towers to get the most accurate location fast. If GPS is available, iPhone displays a blue GPS indicator. But if you’re inside — without a clear line of sight to a GPS satellite — iPhone finds you via Wi-Fi. If you’re not in range of a Wi-Fi hot spot, iPhone finds you using cellular towers. And the size of a location circle tells you how accurately iPhone is able to calculate that location: The smaller the circle, the more accurate the location.
GPS on iPhone is active only when you need it. iPhone powers the GPS unit on and off quickly and automatically, so it won’t adversely affect battery life.
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