These tools can greatly help with doing geographic analysis in Tableau.

Creating Custom Polygons on a Background Image

Creating Custom Polygons By Drawing Directly on a Google Map

Tool to Convert ArcGIS Shapefiles into Tableau Polygons

Extremely fast geocoder (and driving distance finder)

If you are looking for more information or places to start, Alan Eldridge’s fantastic blog The Last Data Bender has great resources, as does http://tableaumapping.bi/ who have long provided pre-built TDEs for many additional geographic data sets.