The GPS system is a precise navigation and positioning system. Developed in 1973 by the Department of Defence (USA), the GPS was originally designed as a military tool to assist soldiers, military vehicles, planes, and ships to accurately determine their locations on Earth. Today, GPS is used widely in military, commercial, industrial, and leisure applications. One of the widest commercial uses of GPS is on street-level route guidance that helps a driver to navigate to an address or to a post-code. This book describes the basic principles of the GPS system and then the design of a microcontroller based GPS data logger device is given in detail, including the full source code. With the help of the device, the coordinates of a person, animal, or a vehicle can be stored on an SD card and then the Google Earth mapping program can be used to display the user track on a street-level map.