I am interested in "Republican free zones". They are seldom completely Republican free, but they are called such because you could have 10 neighbors and not know a single Republican voter. These are places with few or no Republican votes. I will define a Republican free zone a little bit more loosely, as a precinct with less than 5 percent of the two party vote. On the county level, there is only one such location, which is (of course) the District of Columbia in 2018's House election, as well as the 2016 presidential election.
Source: Emily Badger - NYTimes
This is a visualization of the 2016 presidential election. I want to know about the House elections and whether or not more voters live in such a location. I am not asking for a complete list, but I am asking for how prevalent such a precinct was in 2016 and 2018. In the presidential election, it was 3.6%. My data suggests that it was less than that in 2016 and at least that for 2018.
To be clear I want the % of votes cast in such a precinct where data is easily publicly available and candidates of both major parties ran in 2016 and 2018. My guess is that it would be less than the share of voters in the presidential election because there are unopposed congressional elections but not unopposed presidential elections.