Cartographic generalization of the rivers is a very complex process in cartography. Cartographic generalization involves reduction of water flows, their length, width and the density of river basin with the reducing of the map scale. In this study we analyzed the ratio of the density of river basin and the size of the degree of generalization of the maps of different scale. The example is the Velika Morava river basin. Based on the results given here we get to the basic regularities of proportion of the degree of generalization of the density of river basin.