I have an ASCII 2m lidar DTM file which I converted into a raster in ArcGIS with the From ASCII to Raster tool. From this DTM file I would like to calculate the slope and aspect. I have used the spatial analyst -> surface toolbox for this. The DTM has a BNG projection and all values are calculated in degrees. I followed several different tutorials and they all show a same result, a 'equal and smooth' raster with slope or aspect values (ArcGIS and GIScourse).
However, when I try to do this for my DTM raster, I get both 'smooth' parts (left side of pictures) but also what seems like contour lines (right side of pictures). It seems like they follow the lines of the DTM where values change, not really changes in slope etc.
Had anybody had the same problem and/or can anybody tell me what I am doing wrong?