Fraction of people in each city that could potentially be fed locally if all croplands within 50 miles of each city were used for local food production. Based on a typical U.S. diet for multiple years 1900 (A), 1950 (B), and 2000 (C). Each panel uses a different classification of graduated circles to represent population magnitudes to more clearly show the relative importance of population centers.  Reference: Zumkehr and Campbell, 2015.