The Global Positioning System
The Global Positioning System (GPS) is a navigation system that relies on satellites comprised of a set of 24 satellites placed in space by the U.S. Department of Defense. GPS was initially designed for military purposes; however, in the early 1980s, the government began making the system available for civilian use. GPS can be used in all weather conditions, in any part of the world, every day. There are not any subscription fees or set-up costs to use GPS.
How does it work:
GPS satellites travel around the globe every day in an exact orbit. They transmit information about the signal to the earth. GPS receivers receive this information and then use triangulation to determine the user's exact location. In essence, the GPS receiver compares when the signal was sent by satellite to when it was received. The difference in time informs the GPS receiver of the distance that satellite. With distance measurements from a couple of additional satellites, it can identify the user's location and show it on the device's electronic map. The GPS receiver needs to be locked to the signals from three or more satellites to determine a two-dimensional position (latitude and longitude) and track movements. If there are four or more satellites in the view, the receiver can calculate the user's position in 3D (latitude, longitude, altitude, and latitude).