Creating an exclusion layer
I read through the two Dot Density Mapping with ArcMap blog posts, but still do not understand how to actually go about creating the exclusion layer. The areas I want to exclude dots from are on different layers and I can't seem to combine the selected features from these layers in order to create a final exclusion layer. The merge function is not working for these layers. Could you give a step by step explanation of how to set up the exclusion layer?
Mapping Center Answer:
I will assume that the feature classes that contain the things you want to include are all polygons. You can use the Union tool to combine them into one. Assuming that the only thing in each of the feature classes are the areas that you want to be excluded, then the output of the Union tool will be a feature class in which all the polygons are to be considered as areas to be excluded. If the data in the feature classes that will be "unioned" also includes features that should NOT be excluded, then you should add an attribute to each feature class that indicates which feature to exclude. Then in the “unioned” feature class, you can use a definition query when displaying the layer so that only the polygons that should be excluded are displayed,. To speed up processing, export the feature class with the def query to a new feature class and use that as the exclusion layer.
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