There was a huge change in the support for Chicago Mayor Rahm Emanuel from his 2011 election to the 2015 primary, in which he was forced into a runoff with challenger Jesus "Chuy" Garcia.
These maps represent every voter in Chicago with a dot, colored by the candidate they voted for. It shows not only the diminished support for Emanuel, but the drop in turnout from 2011 to 2015.
See this post for more information on how we made these maps.