This is a really useful dataset, especially when combined with tools like mapbox tile mill[0] and qgis[1]. Hours of fun!
Also helpful to that end: the Global Administrative Areas[1] database.
Finally, it would've been impossible to even start getting my head around how to go about these things if it wasn't for this amazing tutorial by Mike Bostock[2].
[0] http://www.the-american-interest.com/blog/2014/03/03/the-noo...