Cartographic Portrayal of Terrain in Oblique Parallel Projection

The visualization of three-dimensional spatial information as oblique views is widely regarded as beneficial for the perceiving of three-dimensional space. From the cartographic perspective, oblique views need to be carefully designed, in order to help the map reader to form a useful mental model of the terrain. In this study, 3D cartographic methods were applied to illustrate directions, distances and heights in oblique views. An oblique parallel projection was used for representing the view in a metrically homogeneous manner and for emphasizing the relative heights. The height was further visualized using directed lighting, hypsographic coloring and contours. In addition, an equilateral and equiangular grid was draped on the terrain model, for fixing the cardinal directions and for facilitating the estimation of distances and surface areas. These methods were combined and analyzed in a case study on a high-resolution DEM covering a national park area. The resulting oblique parallel views provide visual cues for the estimation of terrain dimensions, particularly heights. The results prepare a basis for further research on cartographic 3D visualization.