GPS 152 Portable Navigator is compatible with Garmin's MapSource points of Interest CD. With this optional CD and the GPS 152 Portable Navigator, you add additional marine navaid detail to your unit. It is compatible with the wide area augmentation system (WAAS), a technology designed to improve the accuracy of GPS positioning to about three meters. On the outside, it comes housed in a waterproof case that's about four inches high and five inches wide. A simple keypad at the bottom of the unit makes entering information easy, without blocking your view of the display.