I'm surprised a seasoned forum person has not answered yet. When they create the maps, they manually set in the contour lines in a folder and create the map (at least that what I have gathered from my research). When you load it on to your computer and run installer, it loads all of the map data, and does not give you an option to reduce contour lines. They only way I know of is to have the person with all the map data recreate the map, and to add less contour lines. What I say may be corrected by an old timer though, so take what I say with a grain of salt.