The paper compares aspect maps created from the same elevation data at different resolutions (30m and 30,720m) using two different GIS software programs, Idrisi and ArcGIS. It finds that at the higher 30m resolution, the mean difference between the aspect maps (MDA) is 25 degrees, but at the lower 30,720m resolution the MDA decreases to 3 degrees. Therefore, the aspect maps and resulting flow models produced by the two programs will show a larger difference when using high resolution data compared to low resolution data.