Arlington has GPS navigation systems and services for sale. The GPS, or the Global Positioning System, uses a collection of GPS satellites, maintained in space by the United States government, to accurately fix the position and time of any place on earth, as long as there is unobstructed light of sight for four or more of such satellites. This is freely available for use in all countries, and has indeed been used in many military, civil and commercial applications. This is used for air traffic and increasingly, in vehicles to help navigate unknown routes and roads. GPS devices can be independent handheld devices or car devices, or it may be as an app on the smartphones. Updated maps and navigational services are also available with the GPS service. If it is fore vehicles in Arlington, the kind of device can vary, such as GPS devices specifically for trucks. Maps are also updated on a regular basis for ease of the consumers. Real-time traffic updates may be available.