The GPSMAP 421 is a compact chartplotter that features an ultra-bright 4" QVGA color display along with an improved high-speed digital design for increased map drawing and panning speeds. It's ready to go with a built-in, satellite-enhanced worldwide basemap and an easy-to-use interface designed to help you navigate the open waters with ease. The GPSMAP 421 also accepts BlueChart g2 Vision cards for added features and functionality such as high-resolution satellite imagery, 3-D views and Auto Guidance technology. The GPSMAP 421 basemap contains worldwide satellite images in place of traditional maps. The GPSMAP 421 also comes standard with a high-sensitivity GPS receiver for superior satellite tracking and quicker acquisition times. In addition, the GPSMAP 421 can receive U.S. graphical weather data via optional GXM 51 satellite receiver/antenna. And with an SD card slot, it's easy to add additional maps without connecting to a computer.