Among those of us who love old maps, the good people at the Atlas of Historical County Boundaries project have digitized and uploaded historical information on the shape of American counties.  With this data one can animate how America’s political boundaries have changed since the founding of the Massachusetts Bay and Virginia Colonies.  The above video shows historic county boundaries from 1630 to 1910 (shortly after Oklahoma and Indian Territory joined to form the State of Oklahoma in 1907).  Please note these boundaries show the creation of government-defined geographic units, not necessarily where population is located.

Another great thing about this data is the level of detail available.  For instance, focusing on the monumental changes that Virginia has gone through is quite interesting:

Note the emergence of many of Virginia’s Independent Cities at the turn of the 20th Century.

Things get more interesting when these county files are merged with historical census data. I decided to look at county population dot densities from the first United States Census of 1790 to the recent 2010 Census.  Here, every dot represents 5,000 people:

Dustin Cable is a Policy Associate at the University of Virginia’s Weldon Cooper Center for Public Service where he conducts research on topics that lie at the intersection of demographics, politics, and public policy.
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