What is raster drainage density and how does it compare to traditional drainage density?
Raster drainage density is simply the area of designated stream pixels divided by the total catchment area and represented as a percentage. As such, it can not easily be compared with traditional measurements of drainage density which are calculated as total stream length divided by area (since length is a vector quantity). Raster drainage density should be used with care as it can be very sensitive to grid scale and grid rotation effects. For example, in course DEMs a pixel may be hundreds of metres wide and it is not realistic to assume that simply because a stream is calculated to flow through this pixel that it would have a width equal to the pixel width. A better measure of drainage density is vector drainage density and is automatically calculated when a vector stream network is developed.
