Population Density and Party Preference

The chart is from this article, from which I take this explanation:

The vertical axis shows a congressional district's population density (the number of people who live in each square mile). 

The horizontal axis shows the district's Cook PVI score, which is really just the proclivity of the district to vote Democratic. 

The pattern is clear; congressional districts with low population density (rural) are much less democratic-leaning.

 The same graph is shown in this article, with added information including the following graph:

(Originator of this graph)

Troy concluded that, "at about 800 people per square mile, people switch from voting primarily Republican to voting primarily Democratic." Richard Florida looked in more depth at that finding last November with a broader conversation on what this trend really says about our differing political preferences and needs in crowded cities and leafy exurbs.

I looked for population data related to this idea that the population density of your Congressional District influences the voting choices and found this:

Source

Of course the population of the United States has increased over time, so average population density has also increased. Still the trends are clear that the rural population is decreasing as a portion of the total (and thus there are fewer of the 435 Congressional districts in rural areas) and the suburban population is growing as a percentage of the total (and its Congressional representation increasing).

Source

This last graph suggests that there has been a change in the peri-urban growth pattern since 2006, The rate of population growth in the inner, high density suburbs has increased while that of the more distant suburbs has decreased. The lest dense exurbs growth has fallen below that of the inner suburbs.

Thus there is a trend that may influence the redistricting after the 2020 census, and may influence the ratio of Democrats to Republicans in the Congress after 2022 or 2024. Of course, it is hard to make projections, especially about the future.