This is only the tiniest tip of the iceberg. Just wait till you see some of the other stuff we're working on!
The key here is being able to draw the shapes of individual regions on the map. This lets us do all kinds of fun highlights.
In fact, if you have any ideas about what sorts of map-based visualizations you'd like, please feel free to share them. If they're impossible (or impractical), we can just tell you 
1. Realm color-coding
2. Color-coding by diplomatic status in relation to a selected nation
3. Color-coding by if the region has a lord or not
I'll think of more.
