1. A computer apparatus for topographic processing comprising: storage means for storing a plurality of different topographic map data relating to a same region of a map; selection means for selecting a first one of said different topographic map data; analysis means for selecting partial data of said first one of said different topographic map data relating to a part of the same region, analyzing said partial data of said first one of said different topographic map data in order to determine whether a density of said partial data of said first one of said different topographic map data is more than a predetermined density threshold, and generating the partial data of said first one of said different topographic map data when said density is more than said predetermined density threshold and generating other partial data of a second one of said different topographic map data when said density is not more than said predetermined threshold; and display means for displaying a contour of altitude relating to the topographic map data in the same region of the map based on either one of the partial data and the other partial data guarantee by said analysis means.