How to make a mask to speed up interpolation processing?
Often, there are areas of the input map for which the user does not want to interpolate values (for example, lakes, neighboring counties, areas for which there is already more reliable data). A masking grid layer can be specified to omit those cells from the interpolation. Only those cells of the input map that correspond spatially with non-VOID cells of the mask map are included in the interpolation. Cells corresponding to the VOID cells of the mask map are ignored. For example, VOID cells are colored white, and non-VOID cells are colored black for visualization purposes. Cells with the value VOID will be left out of the interpolation.
Mask grid layers can be created in many different ways:
Draw the mask using the Edit Window drawing tools. Rasterize a feature class containing a polygon or polygons defining the mask area. Use the Recode command on an existing grid layer containing regions that define the mask.
An alternative to masking out a region is to use the Subscene command to crop the data to encompass only the area of interest.