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? This seems to me a bit of a "freshmen fix" but maybe it is the way to go? Any advice?
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.