First, the US Military currently have extra precision based on more accurate clock information that the civilians don't have. I believe that the next generation of satellites do not have this differentiation since with the satellites and a known ground base station you can effectively correct for the lack of accuracy. (This is used in Agriculture where tractors are GPS guided to reduce waste.) Trimble makes a system that can be used for Ag or for Civil Engineering where you are accurate to 3cm.
With respect to all of the claims of accuracy, here are a couple of facts...
1) The GPS 'chips' in your cell phones are not the same as the ones in your TomTom or Garmin and are not as accurate.
2) The basic map data is only accurate to approximately 1.6 meters to 3 meters depending on your location on the earth. They are accurate enough for driving purposes.
3) The GPS system will vary in accuracy based on the weather/sun spots/ ionosphere changes. This is why they have base stations that take 24-48 hours to stabilize before use.
4) Your GPS will be as accurate as the signals it receives from the sats. So if you're in a big city where the tall buildings can interfere with your reception, you're not going to be accurate.
5) Using Cell Tower / Wi-Fi signals to triangulate. Here you can get decent accuracy. At least enough to put you on the map and then you can figure out where you are.... It all depends on the accuracy of the reporting of Wi-Fi hotspots.
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@tomasmcguinness and some general info...
First, the US Military currently have extra precision based on more accurate clock information that the civilians don't have. I believe that the next generation of satellites do not have this differentiation since with the satellites and a known ground base station you can effectively correct for the lack of accuracy. (This is used in Agriculture where tractors are GPS guided to reduce waste.) Trimble makes a system that can be used for Ag or for Civil Engineering where you are accurate to 3cm.
With respect to all of the claims of accuracy, here are a couple of facts...
1) The GPS 'chips' in your cell phones are not the same as the ones in your TomTom or Garmin and are not as accurate.
2) The basic map data is only accurate to approximately 1.6 meters to 3 meters depending on your location on the earth. They are accurate enough for driving purposes.
3) The GPS system will vary in accuracy based on the weather/sun spots/ ionosphere changes. This is why they have base stations that take 24-48 hours to stabilize before use.
4) Your GPS will be as accurate as the signals it receives from the sats. So if you're in a big city where the tall buildings can interfere with your reception, you're not going to be accurate.
5) Using Cell Tower / Wi-Fi signals to triangulate. Here you can get decent accuracy. At least enough to put you on the map and then you can figure out where you are.... It all depends on the accuracy of the reporting of Wi-Fi hotspots.
HTH