If the states in the US were defined by the degree to which people interacted economically, they might look more like this map. People within these state borders are more likely to pass dollar bills between them than with people outside the border. We might think of these as interaction states.

http://www.fastcoexist.com/1681677/a-new-map-of-the-us-created-by-how-our-dollar-bills-move#1