This slim-line GPSMAP 520s Marine Navigator flush-mounts easily in your boat and boasts an ultra-bright QVGA display. The GPSMAP 520s also sports a built-in, satellite-enhanced worldwide basemap and simple, straightforward buttons and menus. You can add the optional BlueChart g2 Vision SD card for even more enhanced features.With just a few buttons and a simple, intuitive interface, the GPSMAP 520s makes navigating virtually effortless. And instead of a traditional basemap, the 520 has a basemap of worldwide satellite images. It also has an SD card slot so you can add additional detailed maps without connecting to a computer.