The GPSMAP 521 is a compact chartplotter that features an ultra-bright 5 inch (12.7 cm) QVGA color display along with an improved high-speed digital design for increased map drawing and panning speeds. ItÆs ready to go with a built-in, satellite-enhanced worldwide base map and an easy-to-use interface designed to help you navigate the open waters with ease. The GPSMAP 521 also accepts Blue Chart g2 Vision cards for added features and functionality such as high-resolution satellite imagery, 3-D views and Auto Guidance technology. View Satellite-enhanced Worldwide Base map: The GPSMAP 521 base map contains worldwide satellite images in place of traditional maps. The GPSMAP 521 also comes standard with a high-sensitivity GPS receiver for superior satellite tracking and quicker acquisition times. In addition, the GPSMAP 521 can receive U.S. graphical weather data via optional GXM 51 satellite receiver/antenna. And with an SD card slot, itÆs easy to add additional maps without connecting to a computer. Add Sonar: Where applicable, the sounder version, GPSMAP 521s, comes with a powerful dual-frequency transducer that clearly illustrates depth contours, fish targets and structures whether youÆre fishing in freshwater or off the coast. The GPSMAP 521 and GPSMAP 521s are also NMEA 2000-certified for easy connectivity with sensors, instruments and future marine offerings. Add Extras with Blue Chart g2 Vision: With the optional Blue Chart g2 Vision SD card, you can add a whole new dimension of exceptional features to your chartplotter. Mariner Eye view and Fish Eye view provide you a 3-D perspective of map information, both above and below the waterline. High-resolution satellite images and aerial photographs help you orient yourself in unfamiliar areas. Auto Guidance technology searches through all relevant charts to create a route you can actually follow ù one that avoids obstacles, shallow water, buoys and other obstructions.