The process is relatively straight-forward, but the average citizen on the street rarely has access to this kind of information in order to determine a cell phone’s location.
First a lesson on how cell phones interact with towers. Cell towers are everywhere. They are what make up the network that we all use to communicate with each other by cell phone. The way you connect with these towers is generally by signal strength and how many people are connected to a tower at that point in time. This means (and what makes triangulation not an exact science) is that you can be standing right underneath a cell tower but really be connected to one five miles away.
Depending upon the cellular carrier’s system, you may be connected to multiple towers at once. Alternatively, as you move around, you change towers. All the while, multiple towers may “see” the phone as it moves.
The way that triangulation can estimate your location, is by taking the tower that the phone is connected to (again, may not be the closest one) and drawing a circle around the tower which would depict the coverage area for the tower. The phone being located is somewhere inside that circle. This process is repeated with the next one to two towers until you are left with overlapping circles. In theory, the phone being sought is somewhere in the middle of these circles. In an urban setting the circles would be small (a few hundred meters), in a rural area, the circles would be bigger.
As stated before, it’s not an exact science. When GPS data is available that is preferable to use. But in those rare cases when it is not, this approximation can mean the difference between a person being in one place, when they say they are in another. A phone’s location can be narrowed down to within 100 meters or less.
