Visualizing The Racial Divide by Jim Vallandingham:

Each city is made up of tracts from the 2010 Census. Census tracts are pushed away from neighboring tracts based on the change in proportion of white and black populations between each neighboring tract.

Tracts that have a similar racial mix as their neighbors form groups. Spaces occur where there is a significant change in the racial makeup between neighboring tracts. The space is proportional to the change in racial composition between neighbors (Read More).