New-generation cell phones combine many devices into one. When traveling, one of the most convenient of these features is the built-in GPS. When visiting a place that you aren't familiar with, getting lost is a lot harder when you have turn-by-turn directions on your cell phone. Even the cell phones that don't have GPS can use cell tower position and distance to calculate your location. Cell phones function by communicating with towers connected to a base station in a configuration called a "cell." As you move through the cell, the base station monitors your cell phone's signal and transfers it to the nearest tower.
Cell phones with GPS receivers communicate with units from among the 30 global positioning satellites in the GPS system. The built-in receiver trilaterates your position using data from at least three GPS satellites and the receiver. GPS can determine your location by performing a calculation based on the intersection point of overlapping spheres determined by the satellites and your phone's GPS receiver. In simple terms, trilateration uses the distance between the satellites and the receiver to create overlapping "spheres" that intersect in a circle. The intersection is your location on the ground.
Finding the Way
Using GPS on your cell phone depends on the phone. Some phones use GPS only for 911 emergency calls. Sophisticated phones are able to receive and display location maps to show roads and more, and to give directions. These turn-by-turn programs are mostly JAVA-based and work with your cell provider's database.