City population data is from the U.S. Census Bureau and Erik Steiner, Spatial History Project, Center for Spatial and Textual Analysis, Stanford University. Data on GitHub. Census demographic data comes from the Minnesota Population Center, National Historical Geographic Information System: Version 2.0 (Minneapolis, MN: University of Minnesota, 2011), http://nhgis.org.
Map made by Jason A. Heppler, Gleaves Whitney, Scott St Louis, Gregory Rose, and Jon Lauck. Code and data on GitHub. Original code borrowed from Lincoln Mullen.
For an explanation of the data, see DATA.md.