A Determination of the most Suitable Cell Size of the Digital Elevation Model to compute the Topographic Factor in RUSLE

Preparation of the topographic factor (LS) map in RUSLE model is a very tedious step because of the complicated effects of topography on soil loss. The objective of this study was to determine the suitable cell size of Digital Elevation Model (DEM) for computing LS factor by the method of Moore and Wilson (1992) in a 5326 ha area، northwest of Tehran Province. Towards this end، cell sizes of 30، 50، 100، 200 and 400 m were derived from the 10 m cell size in ArcGIS 9. 3. The appropriate cell size was selected making use of the criteria of spatial dependence and the coefficient of determination (R2). Results revealed that in the preparation of flow accumulation map، the sinks created in digital elevation models must be resolved. Also، analysis of variograms showed that the calculated LS factor obtained from DEM of 50 m cell size is of the most spatial dependence (0. 613) with the highest coefficient of determination (R2=0. 983). As a result، a DEM of 50 m cell size was found out to lead to the production of a more accurate LS factor map.