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I am working in ArcMap and I have created a choropleth map (using a "population" attribute) that is rendering things basically correct except that when the "population" attribute is null, representing no data, it does not render the associated polygon at all.

I would like the null data polygons to render white with a grey outline, as I have the polygons with data rendering with a shade of purple (depending on the "population" value as mentioned above) and a grey outline.

Is there a better way to go about it other than copying the layer and sticking it under the choropleth layer?

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Well I ended up just creating a new layer from the selection of null data polygons, which works well although is perhaps not the most elegant solution. I am going to leave this as unanswered because it does not precisely answer the question of actually displaying the null data from the same layer the choropleth is built from. – isolier Oct 19 '11 at 7:03

Run a field cal. on all null values and assign them a value of -9999. You can then assign -9999 to 0 as a separate class and change the label to Null.

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This, I assume, would indeed work but I ended up going with something a bit simpler, although perhaps clunkier. – isolier Oct 19 '11 at 7:02

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