How does a GPS know your exact location?

A GPS receiver determines your location by measuring signals from multiple satellites orbiting Earth. Each satellite continuously broadcasts a radio signal that includes the satellite's position and the exact time the signal was sent. Your GPS receiver calculates how long each signal took to arrive, and since radio waves travel at the speed of light, it can determine the distance to each satellite. By receiving signals from at least four satellites simultaneously, the receiver uses a process called trilateration to pinpoint your exact position in three dimensions, including latitude, longitude, and altitude. The fourth satellite helps correct for tiny timing errors in the receiver's clock. More satellites in view generally means greater accuracy.