How does GPS know your exact location?

The answer

GPS works through trilateration: your device receives time-stamped signals from at least four of the 31 orbiting satellites and calculates its position based on signal travel time. Because the satellites travel at 14,000 km/h and orbit at 20,200 km altitude, both special and general relativity cause their clocks to drift by about 38 microseconds per day - enough to introduce 10 km of error if uncorrected. Einstein's equations are literally programmed into the system to keep your navigation accurate.