Using a Global Positioning System

• The Global Positioning System (GPS) is a navigation system based on a network of 24 satellites. Users with a GPS unit can determine their exact location (latitude and longitude) in any weather conditions, all over the world, 24 hours a day.
• GPS satellites circle the earth twice a day and transmit information to the earth. GPS receivers use this information to calculate the user’s location by comparing the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver the distance the user is from the satellite. By calculating the distances from several satellites, the receiver can determine and display the user’s location on the GPS unit.
• Once the user’s position is determined, a GPS unit can calculate other information, including bearing, trip distance, distance to destination, and sunrise and sunset times.
• GPS receivers are accurate to within 15 meters (49 feet) on average. Certain atmospheric factors and other sources of error can affect the accuracy. Accuracy can be improved with a Differential GPS (DGPS) or Wide Area Augmentation System (WAAS).

Some vehicles now come with a built-in GPS unit as an option.