#explainer
A GPS receiver measures arrival times of satellite radio signals and uses them to infer ranges. Combining measurements determines its position and corrects its own clock error. Satellites do not send each phone a ready-made address of its location.
Why four satellites are usually mentioned
Ordinary standalone determination of three-dimensional position and receiver clock error needs at least four suitable measurements. More visible satellites can improve the solution and its availability. Satellite geometry, atmospheric propagation and reflections from buildings affect accuracy; satellite count alone does not guarantee quality.
GPS is not mobile internet
Basic satellite reception does not require sending a position back to satellites or having a data connection. A phone may nevertheless use the internet for maps and assistance data. GPS is a specific American system; devices can also use other navigation constellations, such as Europe's Galileo.
Why a phone can show the wrong street
Buildings can block or reflect signals, reducing the quality and availability of measurements. The map itself is a separate data layer. An incorrect position dot and an incorrect street name or road layout therefore need not have the same cause. Navigation apps combine satellite measurements with other data and algorithms.
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Why clocks matter
Radio signals cross large distances in very little time. A small timing error therefore produces a meaningful inferred-range error. Satellites carry precise clocks, and the control segment monitors their condition and orbits. The receiver also estimates its own clock error, so a consumer phone does not need the same onboard time standard as a satellite.
Key points
- Ordinary standalone determination of three-dimensional position and receiver clock error needs at least four suitable measurements.
- Basic satellite reception does not require sending a position back to satellites or having a data connection.
- Buildings can block or reflect signals, reducing the quality and availability of measurements.
- Radio signals cross large distances in very little time.
Sources & further reading
- GPS operation, accuracy and the distinction between positioning and map data.
- Range and position determination from satellite-signal timing.
Spaceflightpedia. (n.d.). How does GPS work?. Retrieved 17 October 2026, from https://spaceflightpedia.com/article/how-gps-works
article text — CC-BY-SA · ◉ NASA photography — public domain · ✦ AI illustration — marked, generated from sources
