Northstar Model 557 Hi-Resolution Chartplotter with GPS The built-in 32 MB regional background map still offers reliable entry-level use, waiting to be enhanced with C-Map's latest cartography: NT MAXT. With a 640 x 480 pixel screen, chart display becomes 4 times sharper than previously released, reducing eye-fatigue. Fuel management provides tremendous benefits, now more than ever before. With a range of optional fuel add-ons, your Explorer 557 is a powerful travel tool for your boat.