To create contour lines a high quality DEM free of vegetaion and man-made features (DTM) is very beneficial. Contour Lines based on DSM data show a mix of terrain elevation and the height of surface objects, e.g. trees and buildings, and it is difficult to interpret the terrain information. NakedEarth is an ideal base map to generate contour maps representing the shape of terrain over large areas.
The Contour Line Maps based on NakedEarth and SRTM (equidistance of 5m) vary tremendously: only contour lines calculated based on DTM data reliably illustrate the topography.