MI, NC, OH, PA congressional elections 1972-2016: district breakdown by % of votes for Democrats

Inspired by Blake Esseltyn's attempt to visualize MI,NC,OH, and PA redistricting results, I copied congressional election results (democratic votes only) in those four states from gerrymander.princeton.edu into a spreadsheet and broke down district results by percentile. For example, for 1972 Michigan congressional elections we have 19 districts with the following votes % for Democrats (in no particular order):

89.08%, 43.57%, 40.24%, 32.75%, 38.14%, 49.36%, 29.89%, 39.93%, 29.83%, 31.63%, 30.05%, 50.82%, 86.54%, 54.86%, 66.68%, 69.58%, 67.15%, 47.38%, 28.93%.

After breaking down buy percentile, we get:
Districts that got between 0% and 10% votes for Democrats: 0 out of 19: 0%
Districts that got between 10% and 20% votes for Democrats: 0 out of 19: 0%
Districts that got between 20% and 30% votes for Democrats: 3 out of 19: 16%
Districts that got between 30% and 40% votes for Democrats: 5 out of 19: 26%
and so on.

The following are four heatmap charts that visualize Democratic votes breakdown for these fours states. Watch districts gravitating towards 30-50 democratic vote percentiles since 2010.