We've just released a new feature in Tableau Public: geocoding for Congressional Districts. This means that if you have data for Congressional Districts in a state, you can put that on a map in Tableau without needing to define the district shapes and locations. Tableau does all that for you.
For example, here's population by Ohio's Congressional Districts:
One other change you might notice is the new sharing features at the top of the viz preview:
...making it easier to find the link and embed code to your visualization.
I hope to see all kinds of visualizations using Congressional Districts in about a week!