Our most common type of mobile device is the GPS, or Global Positioning System. These are portable tools that are used to identify their own precise position on a map. They do this by communicating with orbitting satalites, and include software that will convert your coordinates on the globe into street intersections on a map. They can offer advice as to how to reach a given destination, right down to which direction to turn when you reach an intersection. They come in varying sizes, but are typically hand-held.