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I'm trying to draw home range maps in ArcGIS 10.1 and am having difficulty displaying them as I would like.

The home ranges are in the form of polygons and many of them overlap. I'm trying to get a display setting that allows all polygons to be displayed at once, particularly where they overlap.

Essentially what I'm trying to do is display the polygons in the same way that the standard primary colour illustration appears, with three overlapping circles of different colours. The important part here is that where the polygons overlap they will combine to make a new colour, thus clearly demonstrating the overlapping area. Another way this is often done is to display each polygon with a unique crosshatching. For instance polygon 1 could have a left-facing diagonal hash, while polygon 2 could have a right-facing diagonal hash. Where they overlap, a cross-hatch pattern would be observed.

Transparency works in relation to other layers in the map, but unfortunately it doesn't seem to work in terms of each polygon within the layer. Same goes for defining the symbology level (essentially they all need to be on the same level).

I've seen this done with many other maps of animal home ranges or other overlapping zones, so I'm assuming there's got to be a way of doing this.

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not sure if i understand exactly what you need, but maybe you need to extract your polygons to individual shape files in order to be able to overlay them and create the effect you want, for this you can use the Split tool (Analysis Tools -> Split). –  A.R Jan 26 '13 at 19:37
    
There's some discussion of colour mixing here but it seems to require Production Mapping and applies only to PDF output. I think you may be looking for On-screen Colour Mixing for Overlapping Polygons which could be something you could put up as an ArcGIS Idea. This might also be a good question for Ask a Cartographer. –  PolyGeo Jan 27 '13 at 1:13
    
@user14629, Can you provide us a link of these examples that you have seen before? I'm sure somebody here will be able to reproduce what you need given a visual example. –  artwork21 Jan 27 '13 at 2:18
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This blog post explains how to compute the distinct overlapping regions and figure out what polygons contribute to the overlap. My thinking is that the attribute you map to the overlap (which is species in the linked example) would be the color. After performing the procedure you would have a layer in which you know all the contributing colors for a region. From there you need to develop a function to map the multiple, overlapping colors into a single new color using some kind of color mixing model. That's my $.02 –  Llaves Jan 27 '13 at 4:26

2 Answers 2

If you are looking for the simple diagonal hatch method you mention, this can be achieved by symbolizing the home range polygons as unique categories. First use the '10% Simple hatch' symbol for all, and then customize the individual symbol patches. For each symbol, click on the Edit Symbol button where you can modify this line fill symbol's color, angle and separation (the offset can also help with multiple overlaps). Unless you have more than five overlaps, using these different settings for each home range should give you a crosshatching visualization that can still be easy to read. (@Llaves link to the blog post is super cool!)

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Thanks for all the help.

Since I only had 7 individual animals I wanted to map, I ended up using the Split tool to separate each individual polygon into its own shape file. Then I was able to set the colour and transparency of each layer separately.

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