In ArcGIS 10.1, I have a DTM and a polygon layer representing urban areas. For processing reasons, I want to exclude the urban areas from the DTM (i.e., setting urban areas to NoData). How can I accomplish that? My guess is that I have to preliminary convert the polygon layer to raster, and then using Raster Calculator. But I am stuck on this latter step.
I found a solution. 1) find a polygon that cover the extent of the whole area; 2) use the ERASE tool, as described here: Performing reverse clip in ArcMap?; the tool will subtract the urban areas extent from the extent of the whole area; 3) use the polygon layers returned by step (2) as mask in the EXTRACT BY MASK tool. The resulting raster will be the DTM with the extent of the urban areas set to NoData.