GPS (Global Positioning System) is a navigation technology that provides precise time and location anywhere, anytime and under any atmospheric conditions, by using the NAVSTAR satellites.GPS is a satellite-based navigation system that works by receiving navigation messages fro satellites and calculating locations. GPS receivers locate the satellites transmitting the incoming signals and use CDMA (Code Division Multi Access) method to identify individual codes. This means GPS system is able to identify each satellite's unique ID to calculate precise location and navigational data.

Many factors affect how accurate your GPS is. The atmosphere, the ionosphere and the position of your receiver could all affect GPS accuracy. Any buildings, natural structures or heavy foliage that obstruct the GPS' view of the sky may decrease the position accuracy. Your GPS accuracy will also depend on your level of clearance with the US DOD.

NAVSTAR is an acronym for Navigation Satellite Timing and Ranging, a name given to the GPS satellite system by the US Government.

There are nearly 30 navigational satellites orbit the Earth and more might be added. Each satellite makes one Earth orbits every 12 hours. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with nominally four Space Vehicles in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight Space Vehicles visible from any point on the earth.