Some smart peeps @ the University of Virginia Weldon Cooper Center for Public Service have built an interactive Geospatial Information Systems database with more than 7GB (one dot per person; 308,745,538 dots) of Census data to show us where US Americans live on a map. Pretty incredible...
A few neat things to note:
1) Natural geographical features of our country that have influenced population centers (rivers, mountains, plains, desert).
2) State, county and city boundaries that have influenced population centers.
3) Streaks of population that are clawing their way westward in ND, SD, NE, KS, OK, & TX.