Latitude lines, which run horizontally around the Earth, allow mariners and pilots to know how far north or south they are from the equator, while longitude lines, which run vertically between the two poles, tell travelers how far east or west they are from the prime meridian. Latitude lines are spaced every 15 degrees between the equator and the North and South Poles. Longitude lines circle the globe beginning at the prime meridian in Greenwich, England, and are also measured in 15-degree segments.
Through latitude and longitude, a traveler can tell his exact position on the Earth by marking one line east to west from the traveler's position and another from north to south. The intersection point is where the traveler is located.
Each degree of latitude and longitude is divided into minutes and seconds. Just as on a clock, each degree has 60 minutes, and each minute has 60 seconds. The seconds may also be divided into tenths, hundredths or thousandths.
Once a position is noted, it may be plugged into a GPS or other mobile device and used to plan routes, figure out estimated arrival times, or track a ship or plane. Websites, such as FlightAware.com, use this technology to do real-time tracking of aircraft.