A New Method of Terrain Representation

HE oldest method of depicting landforms on maps is to draw perspective or side views of mountains or hills placed in their approximate position on otherwise "flat" maps. These representations, ranging from the crude "sugar loaves" of ancient maps to the sophisticated symbolism of present-day physiographic or landform maps, have one major defect in common: the side view of a landform having a vertical dimension requires horizontal space, and on an ordinary map horizontal space is reserved for planimetric position. For example, if a single mountain is drawn on a map as seen from the side or in perspective, the peak or base and most or all of the profile will be in the wrong place planimetrically. This fundamental defect of landform maps has been recognized by the cartographers who draw them but has, properly, been justified on the ground that the realistic appearance obtained more than outweighs the disadvantages of planimetric displacement.' On the other hand, map users and makers are not consistent in their concern about this error. On a small-scale map deviations from correct planimetric positioning that on the earth might amount to tens or scores of miles bother few, but an error of a mile or two on a large-scale map seems to be quite unacceptable. Whatever the reason, there have been few physiographic maps at topographic scales, and their rarity is certainly not due to lack of knowledge of terrain. Planimetric displacement becomes serious at large scales. Raisz states: "For this reason [planimetric displacement] landform maps are not recommended for any larger scale than 1: 1,ooo,ooo. For larger scales the map should be transformed to an obliquely-seen block diagram.12 One way to reduce planimetric displacement as scale increases is to adopt a high oblique angle of view. The authors had discussed this possibility but had not had an opportunity to put it to a test. When the Environmental Protection Division, Quartermaster Research & Development Center, Natick, Mass., indicated interest in having a landform drawing prepared of the Camp Hale area in Colorado at the scale of 1: 50,000, a proposal was