Originally Posted by JoeT
When you are indoors, you likely aren't able to receive the GPS signal. When that happens, the iPhone goes back to the V1-style cell/WiFi triangulation.
As far as an error of 50-100 feet - that's reasonable for GPS.
...the same reason XM and Sirrus have trouble indoors.
The GPS uses a
constellation of at least 24 (32 by March 2008)
Medium Earth Orbit satellites that transmit precise
microwave signals, that enable GPS
receivers to determine their
location, speed, direction, and time.