Cartographic Contouring with Computer and Plotter

Digital models of height points approximate the earth's surface or depict the spatial distribution of other geographical or geological phenomena. Digital models of the earth's surface (DTMs) are distinct from those representing thematic phenomena (DEMs) and require different treatment. Algorithms for computer-assisted contouring based on digital models should be adapted to the type and character of DTM at hand; general-purpose contouring algorithms have dubious advantages. This paper describes the algorithm of a computer program for the interpolation of contours into a regular grid of height points; suggests a solution to the “saddle problem,” based on geomorphological considerations; and demonstrates the adaptation of contour flow to the structure lines of the relief. The details of computer-executed “cosmetic” treatment of contours follow, including algorithms for labeling contours, generating index contours, and notating spot heights.