1. A marine navigation device comprising: a location determining element configured to determine a current geolocation of a marine vessel on a first body of water; a display; a memory element configured to store sonar data for substantially all of each of a plurality of bodies of water; and a processing element in communication with the memory element and the display, the processing element configured to— access the sonar data from the memory element corresponding to the first body of water, calculate bottom hardness shading data based on the sonar data, generate a map representation of at least a portion of the first body of water corresponding to the current geolocation, the map representation including shading derived from the calculated bottom hardness shading data, and control the display to visually present the map representation.