Abstract: In this paper, based on review of the studies on methods and techniques of terrain information description, topographic unit diversity index (TUDI), a new concept and quantification method, was proposed. The diversity index integrates several terrain parameters, e.g., elevation, slope, slope position, slope aspect, water confluences and distributions information. By combining the algorithms of the topographic position index and the topographic wetness index, using layer overlay analysis method and appropriate indicators for classification and grading, TUDI algorithm re-classifies the types of topographic units, and then calculate the TUDI using the neighborhood statistics and analysis method. The results of the experiment in Sichuan Province as a test region using DEM (100 m×100 m) and waters distribution data (1:250,000, 2005) show that TUDI is a comprehensive index, revealing the complexity and variations of the true surface. In the process of calculation, the topographic units were divided into 13 different types. The topographic unit diversity index was calculated with the statistics window radius set to 900m based on division results of the topographic units. The areas with diversity index value less than 0.5 cover around 11 percent of the whole region; the areas with the value more than 0.75 take up as much as 57 percent. Basically the results of the calculation agree with the topographic features of the study areas. In addition to the experiment to test the reliability of the algorithm, the advantages and disadvantages of it were also evaluated. This research provides a good basis for constructing a conceptual system of DEM-based topographic attributes, as well as for the spatial analysis of terrain information from micro to macro scales.

Key words: DEM, GIS, topographic position index, topographic unit, topographic wetness index