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Billions of phones and cars rely on a satellite-based system to figure out their exact location on Earth, using signals from satellites orbiting thousands of kilometers overhead.

How does GPS actually calculate a device's position?

By measuring the time delay of signals from multiple satellites to calculate distances and triangulate a position ✓
By having each satellite take a photograph of the ground below
By bouncing a radar signal off the device and measuring the echo

By measuring the time delay of signals from multiple satellites to calculate distances and triangulate a position
Each GPS satellite broadcasts its precise location and the exact time the signal was sent; a receiver measures how long each signal took to arrive from several satellites at once, and combines those distances to pinpoint its own location through trilateration, and because the calculation depends on split-second timing, GPS satellites carry atomic clocks accurate enough to matter even at nanosecond scales.

GPS works through trilateration. Each satellite broadcasts its own precise position and the exact moment its signal was sent. A receiver compares departure and arrival times to calculate distance to each satellite, and once it has readings from four or more, it solves for its own location plus a time correction. Because radio signals travel at light speed, tiny timing errors become large distance errors, why satellites carry atomic clocks accurate to nanoseconds.

A camera-based system would need huge bandwidth and fail through clouds or at night. A radar-echo approach would require actively scanning for each device, impractical at that range for billions of devices at once.

Relativity matters here: satellite clocks run faster due to weaker gravity at altitude but slower due to orbital speed. Engineers correct for both, or GPS positions would drift by kilometers within a day.

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