GPS (Global Positioning System) is a satellite-based navigation system operated by the United States. A receiver works out its position by measuring how long signals from at least four satellites take to arrive. The wider term for such systems is GNSS, which also includes Russia's GLONASS, Europe's Galileo, China's BeiDou, and India's NavIC.
Why it matters
GPS provides location and very accurate time, used for maps, delivery tracking, aviation, and for synchronising networks and servers. The device only receives signals; it does not transmit its position to satellites. Phones typically reach accuracy of a few metres in open sky. Buildings, tunnels, and dense city streets can degrade the signal.
Phones use A-GPS (assisted GPS), which downloads satellite data over the network and uses Wi-Fi and cell towers to get a quick first fix. Without assistance, a cold start can take much longer.
Example
Each satellite sends its position and an exact time stamp. Because radio waves travel at about 300,000 km per second, a delay of 0.07 seconds corresponds to roughly 21,000 km. Combining four such distances solves for latitude, longitude, altitude, and the receiver's clock error.
Common mistakes
- Assuming GPS needs mobile data. The satellite signal alone works without it.
- Trusting indoor GPS readings.
- Treating the displayed accuracy circle as exact.
- Forgetting that location data is sensitive and apps should be given permission carefully.
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