Global Positioning System
The Global Positioning System (GPS) is a satellite navigation system.
There are several places where GPS information can found. It can be very useful for forensic investigations in certain situations.
Digital Camera Images with GPS Information
Some recent digital cameras have built-in GPS receivers (or external modules you can connect to the camera). This makes it possible for the camera to record where extactly an photo was taken. This positioning information (latitude, longitude) can be stored in the Exif metadata header of JPEG files. Tools such as jhead can display the GPS information in the Exif headers.
Cell Phones with GPS
Some recent cell phones (e.g. a Motorola EZX phone such as the Motorola A780) have a built-in GPS receiver and navigation software. This software might record the paths travelled (and the date/time), which can be very useful in forensic investigations.