Know your Illinois legislative district? A great resource to look it up is IllinoisAtlas.com You'll find fascinating (at least they fascinate me) political, economic, and demographic maps of Illinois here.
A friend on the Hill sent me a great map displaying generic names for soft drinks by county. We say "pop" on the West Side and I had no idea there was an alternative for a long time.
Anyone trying to understand data displayed through maps must first read Mark Monmonier's book How to Lie with Maps. You can bamboozle yourself with map-displays besides getting suckered by the mapmakers.