How do map applications such as GPS determine your location?

• A. Satellite data
• B. Local manual input only
• C. Weather data from nearby stations
• D. User's memory without any data

Answer: (A)

GPS determines your location by using signals from satellites. Each satellite broadcasts a precise, time-stamped signal and its known orbital position. Your device measures how long the signal takes to arrive, which gives a distance to that satellite. With signals from several satellites, the device solves a geometric problem to pinpoint where you are on Earth. The system relies on satellite timing and positions to provide a global reference frame, and it needs multiple satellites to get an accurate 3D fix (including altitude) and to account for the receiver’s own clock error. Weather data or guessing from memory can’t supply that real-time, absolute positioning information.