GPS is a system of triangulating the position of an object on earth. In order to complete the triangulation process you need three satellites in view of your position. Up until 1993 the GPS system was purely military in nature and not open to civilian access.
In 1994 the final block II satellite was set into orbit to make a total of 24 satellites in orbit. Today we have 30 satellites in orbit, and the real name for the GPS is the NAVSTAR system. GPS simply sounds better and thus was adopted for consumer marketing.
What does all this have to do with the accuracy of GPS?
GPS systems require you to be within sky range of three of these orbiting satellites in order to receive their signals. GPS units use the satellite locations to calculate your current position. There may be times even now when your just not in the right spot, and you can duck under the satellites. However, in general a GPS is accurate up to a few thousand feet of your current position at any given time. In order to use trilateration to calculate you height you need a fourth satellite to be in view.
Cell phone GPS systems,
A cell phones GPS actually works on a different principle then this, and thus can be less accurate. A cell phone measures the strength of your signal to fixed location towers. Comparing this signal strength to what range it would expect from that signal strength.
As you pass from one tower to another, this signal is transferred to the closer tower, and you are switched to a new cell range. By calculating the signals strength and time to arrive at multiple towers it is possible to triangulate your signal, and direction of movement.
However, since this method requires you to be in range of cell towers, the only time it can be used is when your phone is on, charged, and in range of a tower. If your hiding from some one, don't use your phone. You should also remove the battery or they can turn it on.
Cell phone GPS remote powering,
Cell phone GPS can be turned on remotely even if your battery is dead. The only way to ensure you are not being tracked is by removing the battery, or not having the cell to begin with. If you pissed "big brother off" you may as well dump the cell, but just how close can they come to your exact position? Cell phone carriers are required to be able to provide your location to within 100 meters. They may however be more accurate at times.
GPS location and mapping,
If you're wondering how accurate your GPS map is, it should be about the same, as the tracking, 100 meters or 328.1 feet. So when your getting those directions off your phone, it is going to be deadly accurate as to your location. However, it might not be so accurate as to what stores are nearby. Some stores open, close and change hands very often. This results in becoming misinformed from time to time about the existence of a store in your area.
Summary,
To summarize your cell phone can track you to within approximately 328 feet. This function can be turned on remotely by police or other government agencies. Your phone will be extremely accurate when working as a GPS navigator. Some model phones may allow you to turn tracking on and even lock it for keeping tabs on your kids. If you don't want to be tracked down then remove your cell battery, and If you never want to be found, why do you have a cell?
opcorn:
