The Global Positioning System (GPS) is a space-based global navigation satellite system. It provides reliable positioning, navigation, in all weather, day and night, anywhere on or near the Earth.

GPS is made up of three parts: between 24 and 32 satellites orbiting the Earth, four control and monitoring stations on Earth, and the GPS receivers owned by users. GPS satellites broadcast signals from space that are used by GPS receivers to provide three-dimensional location (latitude, longitude, and altitude) plus the time.

GPS has become a widely used aid to navigation worldwide, and a useful tool for outdoor activities, including hill walking, hiking, geocaching and waymarking.