Ask A Cartographer

Representing overlaying polygons on a 2D map

September 17 2007 | 0 comments
Categories: Symbology

Sometimes we have polygon layers in which the features are allowed to overlap (sometimes considerably!). What is the best way the represent the features in such a case? Creating hollow fills makes the map very confusing.

Mapping Center Answer:

It really depends on what you need to show, and that’s determined by what your data represent. So without knowing that, I cannot give you a specific recommendation. However, here a couple of additional strategies you may find useful:

1. Using transparency.
a. At the layer level if you have an attribute that can be used to set up definition queries, which will enable you to create several layers that symbolize, for instance, different time intervals. You could symbolize each layer with transparency and with distinct colors so users could tell which features belonged to each timeframe. To set this transparency use the Display tab on the Layer properties dialog box.
b. In the Symbology tab of the Layer Properties dialog box, you can set transparency for each feature using the Advanced button. This works based on your data having a field for the transparency percentage, so the data would need to be set up to drive this symbology.

2. Use the Union tool to geoprocess the data so that the overlaps are distinctly defined (the tool will work with just one feature class as the input). Then you would likely need to create an attribute that conveyed the nature of the features based on how they were overlapped.

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