I found a document (pdf) on the US Census Bureau site with data on the mean and median population centers of the United States over time. Unfortunately they didn’t stick it on a map so one can get a real sense of the slow south west migration. Fortunately this provided me with a good excuse to learn the google maps API and put the points on a map.
I’ve put the maps up here. I’m not sure I expected the median and mean to be so similar (though unfortunately there’s a hundred years less data for median). The mean ends up further west than the median because the distance of the west coast amplifies the weight of its population.
I was actually looking around the US Census site looking for some interesting data to build a Treemap with, but didn’t find anything yet with a two level hierarchy that didn’t end up at the county level. Got any ideas of something that could be interesting in treemap form?