The Global Positioning System (GPS) is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. The GPS program provides critical capabilities to military, civil and commercial users around the world. In addition, GPS is the backbone for modernizing the global air traffic system. The Automatic Identification System (AIS) is an automated tracking system used on ships and by Vessel Traffic Service (VTS) for identifying and locating vessels by electronically exchanging data with other nearby ships and VTS stations. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport. Information provided by AIS equipment, such as unique identification, position, course, and speed, can be displayed on a screen or an ECDIS. An Electronic Chart Display and Information System (ECDIS) is a computer-based navigation information system that complies with International Maritime Organization regulations and can be used as an alternative to paper nautical charts. An ECDIS system displays the information from electronic navigational charts (ENC) and integrates position information from the Global Positioning System and other navigational sensors, such as radar and AIS. It may also display additional navigation-related information, such as Sailing Directions and fathometer.