Learn in the textbookSystems for Finance and Social Infrastructure
DefinitionGPS (Global Positioning System, 全地球測位システム) is a system in which a receiver picks up signals from several satellites orbiting the Earth and works out its own position.
ExplanationEach satellite keeps sending signals stamped with the exact transmission time, and the receiver computes its distance to the satellite from the gap between that time and when the signal arrived. Combining the distances to several satellites fixes latitude, longitude and altitude to a single point. Japan also uses quasi-zenith satellites (準天頂衛星, the Michibiki system) to supplement GPS; their orbits keep them high in the sky over Japan for long stretches.
AnalogyIt works like counting the seconds between a lightning flash and the thunder to judge how far away the storm is: the signal's travel time becomes a distance.
Memory hookG = Global, P = Positioning: the name itself says it fixes your position anywhere on the globe.