These maps are created by plotting the residential latitude and longitude of all Democrats and Republicans, as they are identified on state voter files from 2016 and 2017 (note some states do not have party registration and so the party is assumed from primary voting). Voters who are not Republicans or Democrats are not mapped.  Each map represents a Core Based Statistical Area (CBSA) based on 2015 definitions.   In preparing the maps, the lower and upper 1.5 quantile of both latitudes and longitudes in each CBSA were removed in order to remove errant geocodes.  The maps were created using ggplot2 in R.  The header of this page is map of every Republican and Democrat in the United States.