GPS has become common as your car stereo was a few years back, and many take for granted the previously solely-military use only technology. As the technology has come out in many types such as hand-held and built-in types for automobiles, they have also had their fair share of criticism from drivers and people alike. First, these systems only work flawlessly in areas that have been extensively mapped and referenced with proper equipment. Meaning a mean error of around a few meters is to be expected. For something that is hailed to be something that would take the fear out of going to an unknown place with the right directions, it is quite contrary for it’s abilities.
To go deeper into the said or expected error, the main reason being, the technology is still mainly intended for military use only and the only people with the proper equipment to use GPS with pin-point accuracy to within less than a few meters is, guess who, the military. The GPS system used by civilian and government agencies is the same, the difference is in the way they obtain data. Civilian GPS gadgets get signals from at least 2 or three satellites in space which are used for reference (the very best collaborates that information with one ground station and then factors in the positional reading from the two satellites triangulating the current position.
All civilian versions have a built-in error factor which eliminates the use of civilian GPS technology for insurgent or other terrorist activities. The military use more than one satellite for referencing plus cross-referencing with two ground based stations making their positional data more accurate to within a few inches, and they also have sophisticated algorithms that computes the exact target coordinates.