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?

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closed as off-topic by PolyGeo Nov 27 '17 at 21:48

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  • If the east side of your area has a stair-like relief (likke paddy fields), your result seem normal – GISGe Nov 21 '17 at 12:02
  • @GISGe Unfortunately, the east side does not have this stair-like relief, that is the problem. – AnoukStats Nov 21 '17 at 14:21
  • Then you should maybe check the quality of your DTM and how the conversion from lidar was made, because the stairs seem to be present in your data. Using a category-based symbology instead of this smooth gradient will make the pattern more visible. – GISGe Nov 21 '17 at 14:34
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    When converting to raster specify cell type as FLOAT, not INTEGER. – FelixIP Nov 21 '17 at 17:14
  • Did you try to import your lidar data as vector points and create a DTM from it and then run aspect/slope? – alecsx Nov 22 '17 at 9:50