How does GPS know your location?

GPS receivers compute location via trilateration using signals from satellites. Each GPS satellite continually broadcasts its precise time and position. The receiver notes how long each signal takes (at light speed) to arrive, giving its distance to that satellite. By measuring the travel time from at least four satellites, the receiver solves for its 3D position (latitude, longitude, altitude) and clock offset. Mathematically: distance = speed of light × time delay. Three distances fix a point in space; the fourth corrects timing errors. In sum, GPS finds where you must be to have those measured distances to the known satellite positions, thus pinpointing your location on Earth.