What is the global positioning system (GPS)?
GPS is a global positioning system designed for use for the wider public to help guide and show our real-time location.
A GPS system works by receiving signals from nearby satellites.
These messages tell two things, the exact location of the satellite as it sent the message and the exact time on the satellite.
The only way to know such exact time is with an atomic clock, requiring an atomic clock on both ends, or a fourth satellite nearby- the fourth satellite allows for a complex equation to be solved as all unknown data points are given in a situation with four satellites.
Without four satellites a 2d location is given or a 3d Location is given with your height assumed as sea level, if at sea level this will be very close to accurate if not, it will be extremely inaccurate.
The Gps will triangulate your position with trigonometry- as shown in the picture a triangle can be drawn between the GPS device and the satellites thus giving an exact location of the GPS device