How does GPS calculate your location?

GPS works using a constellation of satellites orbiting about 20,000 kilometres above Earth, each continuously broadcasting its position and the precise time from an onboard atomic clock. A GPS receiver in your phone listens for these signals and measures how long each took to arrive, which reveals its distance from each satellite. By combining distances from at least four satellites, the receiver can pinpoint its own location in three dimensions and correct its clock. Because the signals travel at the speed of light, even a tiny timing error would cause a large position error — so GPS must account for effects predicted by Einsteins relativity, since the satellite clocks run slightly faster than clocks on the ground.