Digital terrain analysis based on DEM

The digital elevation model (DEM), an important source of information, is usually used to express the topographic surface in three dimensions and imitates the essential natural geography. Now, DEM has been applied in physical geography, hydrology, ecology and biology and when connected with topographic attribute extraction, in watershed and flow path analyses. The study has analyzed the digital elevation data sources and their structure, the arithmetic of terrain attribute extraction from DEM and its application as well as DEM's error and uncertainty algorithm. The Hayachinesan mountain area (in Northeastern Japan) was chosen as the research site and the focus was on terrain analysis and the impacts of DEM's resolution on topographic attributes using TNTmips GIS software (developed by MicroImage Inc., USA) and “digital map 25000”(published by the Geographical Survey Institute of Japan in 1998). The results show that: ① DEM is a very effective tool for terrain analysis; many terrain attributes can be derived such as slope, aspect, slope type, watershed, standard flow path and so on; these attributes can be displayed with both image and attribute databases with the help of GIS; ②DEM's resolution has a great influence on terrain attributes; the following details are shown: (a) DEM resolution has a significant effect on slope estimation: the average slope becomes smaller and the standard deviation larger when DEM resolution changes from fine to coarse and the different impacts of DEM's resolution on different slope ranges can be classified into three gradient classes: 0-10 degree (underestimated slope), 10-35 degree (overestimated slope) and more than 35 degree (little impact on slope estimation); (b) DEM resolution has little effect on aspect estimation, but flat areas become larger when DEM resolution changes from fine to coarse; and (c) the quantity of hydrologic topography information declines as DEM resolution decreases.