/ˌdʒiː piː ˈɛs/
noun — "satellites that tell you exactly where you are anywhere on Earth."
Global Positioning System (GPS) is a constellation of satellites, ground stations, and receiver technologies designed to deliver accurate positioning, navigation, and timing (PNT) information anywhere on Earth. Developed originally by the U.S. Department of Defense for military applications, GPS has become a ubiquitous component of civilian, commercial, and scientific systems. The core functionality relies on measuring the time delay between signals transmitted by multiple satellites and received by a GPS receiver. Using these measurements, the receiver calculates its three-dimensional position (latitude, longitude, and altitude) and precise time.
The system comprises at least 24 operational satellites in medium Earth orbit, forming a near-constant global coverage network. Each satellite broadcasts a unique signal containing orbital parameters, atomic clock timing, and system status. Receivers use trilateration by comparing the time-of-arrival of signals from at least 4 satellites to solve for position and clock error simultaneously. Advanced receivers may use additional satellites to improve accuracy, apply differential corrections, or integrate data from other Global Navigation Satellite Systems (GLONASS, Galileo, BeiDou).
Technical characteristics of GPS include:
- Position accuracy: civilian receivers achieve 3–5 meter accuracy under clear sky conditions; military or augmented systems can reach centimeter-level precision.
- Timing precision: atomic-clock synchronization allows timing errors as low as 10 nanoseconds in some receivers.
- Coverage: continuous global visibility provided by satellite constellation geometry.
- Signal structure: satellites transmit at 1575.42 MHz (L1) and 1227.60 MHz (L2) with distinct pseudo-random codes to allow multiple receivers to distinguish signals.
- Integration capability: can be combined with inertial measurement units (IMU), differential corrections, and augmented systems for improved performance.
In practice, GPS works by continuously receiving signals from multiple satellites. The receiver measures signal travel times and computes distances to each satellite, solving a system of equations to determine position and synchronize its internal clock. Applications span from turn-by-turn navigation in vehicles, aviation and maritime navigation, precision agriculture, geodesy, and scientific research like earthquake monitoring. Mobile phones and IoT devices increasingly rely on GPS combined with Wi-Fi and cellular networks for hybrid positioning.
Conceptually, GPS is akin to triangulating one’s location on a global scale by using the precise timing of distant, synchronized clocks in space. Each satellite acts as a fixed point in a three-dimensional lattice, and the receiver computes its exact location by measuring distances from multiple points. The system abstracts complex orbital mechanics, signal propagation, and relativistic effects, presenting an instantaneous and precise position to the end-user.
An intuitive metaphor: GPS functions like a digital sextant combined with synchronized watches in the sky, where each satellite’s timing acts as a beacon, guiding a receiver anywhere on Earth to its exact coordinates with remarkable accuracy and reliability.