DESCRIZIONE
A marine navigation device comprises a location determining element, a display, a memory element, and a processing element. The location determining element determines a current geolocation of a marine vessel on a first body of water. The display displays a map representation. The memory element stores digital elevation model data and sonar data for a plurality of bodies of water. The processing element is in communication with the memory element and is configured to select the digital elevation model data or the sonar data from the memory element corresponding to the first body of water, calculate contour line data, the contour line data determining a plurality of contour lines, update the contour line data by selectively removing at least a portion of the contour lines, and generate a map representation including contour lines derived from the updated contour line data, and control the display to visually present the map representation.