GPS finds your position by measuring how long signals from satellites take to arrive. Signals from at least four satellites allow the receiver to solve for latitude, longitude, altitude and its own clock error.
Satellites send time-stamped signals
Each GPS satellite carries an atomic clock and broadcasts its position and the exact time a signal was sent. A receiver compares that timestamp with the arrival time measured by its own clock. Since radio signals travel at nearly the speed of light, a small timing error creates a position error.
The receiver does not need to send a signal back to the satellites. It listens, computes several candidate distances and searches for the point where the spheres around the satellites intersect.
Why four satellites help
Three ideal distance measurements could locate a point in three dimensions, but the receiver’s inexpensive clock is not perfectly synchronised with the satellite clocks. A fourth satellite provides the extra equation needed to solve for clock bias as well as position.
More satellites improve geometry and allow the receiver to reject inconsistent signals. Buildings, reflections and atmospheric delays can still reduce accuracy.
GPS is one part of a larger system
GPS is the United States system; other constellations include Galileo, GLONASS and BeiDou. Phones often combine several systems, Wi-Fi and motion sensors. Maps then match the position to roads or places, but the underlying measurement is timing and geometry.
The blue dot is therefore not magic. It is a continuously updated calculation built from signals, clocks and models of Earth.
Why your phone can be wrong near buildings
Signals can bounce from glass, concrete and metal before reaching the receiver. The phone then measures a longer path than the direct path and places you slightly away from the true position. Combining satellite systems, motion sensors, Wi‑Fi and map matching helps reduce the error, but no calculation can recover information that the environment has blocked.
Sources and evidence
- GPS.gov — GPS basics ↗
Satellite timing, ranging and position accuracy.
- NASA — How GPS works ↗
Space-based navigation and timing context.
Sources consulted: 9 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Explained trilateration and the fourth-satellite clock correction. Added a subject-specific example or limitation to strengthen reader value.