The New York Times (link) uses two histograms to show us the geographical distribution of college graduates today compared to 1970. The histograms clearly and forcefully demonstrate two points: the almost three-fold increase in the concentration of college graduates in metropolitan areas, and the wider spread in geographical preference. In other words, we find that the shape of the distribution (in particular, the width) and the mid-point of the distribution have both shifted in those decades.
Readers must be careful about interpreting the colors, which are keyed to relative scales. Every single orange square on the right chart represent a higher percentage of college graduates than the single orange square on the left... this is because of the massive increase in the number of adults with college degrees over this period of time.
I'd suggest two small improvements. Arranging the histograms vertially makes a huge difference:
On the maps, I'd get rid of the gray dots. The point of the maps is to show where the graduates are flocking to and where they are not favoring. The gray dots on the other hand serve mainly as a geographical lesson of where the metropolitan areas are on the U.S. map.
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