Knowledge of local topography is necessary for many tasks in climatology. For this task, topographic maps containing contour lines can be used. Nevertheless, a spatial conception of the situation is often difficult to obtain. Assistance along these lines is provided by the "digital elevation model" (DEM), which is also necessary for many applications in geographic information systems (GIS).

The digital elevation model of the Baden-Württemberg Office for Land Surveying contains coordinates for the position (Gauss-Krüger system) and elevation (m above sea level) of nearly 15 million points in a regular raster of 50 m for the entire land surface of the state. In the open countryside and in built areas the elevation data are determined by the ground level, while in forested areas the elevation data represent the top level of vegetation (i.e. tree tops). The level of precision amounts to +/- 2 to 3 m in topographically-consistent areas. The data comes from the years 1971-1981.

With the help of interpretive programs, contour plans as well as the size and direction of land inclinations or surface curvatures can be derived from the data. Especially descriptive are perspective views produced from the data, in which the direction and angle of viewing (i.e. elevation) can be determined at will. Some of these interpretive programs (e.g. SURFER) are also available for normal PCs.

Figure 4/29a bis 4/32 show several examples using raster data from the DEM of the Office for Land Surveying.

In addition to the ability to generate virtually arbitrary spatial depictions of areas using digital elevation models, the elevation model can be consulted for more in-depth uses in the realm of urban climatology.

The digital elevation model can serve to translate representative data from relatively few measuring stations into surface-covering climatic maps (see also Chapter 5.3) (GERTH, 1986).

For example, the German Weather Service in connection with the Climate Atlas of the Stuttgart Regional Association carried out a one-year measurement program at 12 temporary measurement stations. Locations were chosen so that the measurement stations represented areas of various land uses, altitudes, and special topographical situations (e.g. valley floors, slopes, and high spots).

Theme-specific climatic maps for individual climate elements could then be developed statistically with the help of the digital elevation model. Using the stations located on open land, a height distribution of the climate data from the relatively uninfluenced areas was produced and carried over to the entire study area with the help of the digital elevation model. By means of the land-use map, consideration was given to the measured average deviations of local influences relative to the general altitude-specific distribution. Thus for example the relative coarseness of the ground surface – determined by buildings, plants, and relief – brings with it changes of various strength in the wind field. Temperature increases caused by development (i.e. heat islands) were necessary to account for, as were smaller temperature decreases from forests and narrow valleys.