Effect of rounding off elevation values on the calculation of aspect and slope from a gridded digital elevation model

Slope and aspect derived from digital elevation models are important variables used regularly in geographical information systems for modelling purposes. Digital elevation models (DEMs) have become a very common and widely used source for creating slope and aspect map surfaces. However, quite often these map surfaces are created and used without due consideration being given to the accuracy of the DEMs and the algorithms used to derive slope and aspect surfaces. The purpose of this paper is to show the flaws in some of the algorithms used to generate aspect and slope information from gridded digital elevation models and to make users aware of problems or errors that may be encountered. The research shows that the precision to which elevation values are stored in a DEM strongly influences the derived products of aspect and, to a lesser extent, slope.