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While you can't split the default locations defined in Tableau, you can draw customized polygons on top of any map (or image). Here's a good article that splits a state into several areas: Creating Polygon-Shaded Maps | Tableau Software. As you'll see, you need to have latitudes and longitudes in your data, for that this blog is superb: Tableau and Behold! | Tableau tools, secrets and examples
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