Originally Posted by domenic72
U beat me to the punch!! Was just going to say that it's logically impossible to have every address mapped to the correct coordinates...especially in rural areas where lots sizes vary immensely. I'd be a little disappointed if the gps was off by 300 feet in an urban downtown area but for rural, 300 is better than I'd expect.
There's also a huge difference between the GPS being off by 300 feet and the mapping software being off by 300 feet.
Typically, the GPS accuracy is within 3 meters, per the DOD specifications. If you are triangulating with cell towers, it's even less accurate - generally accurate within the distance from your location to the cell tower to which you are connected.
The mapping software, however, is also subject to accuracy issues, and often times, that alone accounts for the 300 foot discrepancy. On my first GPS, a Magellan, the original software was off by 40 feet e/w, but spot on n/s. I could be driving north or south on a major road and the GPS would show me 40 to the west of the road, but if I were driving east or west, it was dead on. A subsequent upgrade of the maps fixed it.
So the 300 foot leeway could easily be the software, OR the GPS or a combination. You could always verify your location using Google Maps, BB Maps, Windows Live Search in addition to NavTeq, etc. Check the location with various software tools to determine what is really going on. I'd say that if they are all off by about the same amount, the problem could be the GPS... but generally, I'm guessing the inaccuracies are due to the mapping software.