Suburban Sprawl - A Red-stater's best friend

Dave Troy has a couple of fascinating charts showing voting patterns vs population density  from this election - and the results should be pretty alarming for Republicans.
First, the election results (click to embiggen. A lot)

Note that below 800 people per square mile, people vote Republican, but above it, people vote Democratic. (Ignore the x-axis scale changing at 190 - otherwise the chart would get huge).
Or, to put this slightly differently, any densely populated area will vote Democratic.  But, we pretty much knew this, i.e., your default election results tend to show that the sparsely populated states are all Red, and the highly populated states are all blue (with the rest somewhere in between)

Looking at this a wee bit deeper though makes things a whole lot more interesting.

I'll let Dave explain this himself

Studying this graph, two important facts are revealed. First, there are very few cities in red states. Second, the few dense cities that do exist in red states voted overwhelmingly democratic.

Atlanta, New Orleans, St. Louis, Dallas, and Indianapolis are all in red states — and they all voted blue. And there are no true “cities” in red states that voted red. The only cities in red states that didn’t vote blue were Salt Lake City and Oklahoma City. And by global standards, they are not really cities — each has population density (about 1,000/sq. mi.) less than suburban Maryland (about 1,500/sq. mi.).

Historically, one can argue that red states have disproportionately affected election results by delivering a material number of electoral votes.

Red states simply run out of population at about 2,000 people per square mile. St. Louis is the only city that exceeds that density in a red state. It voted overwhelmingly Democratic (82.7%). In contrast, blue states contain all of the country’s biggest and densest cities: Washington DC, New York City, San Francisco, Baltimore, Milwaukee, Philadelphia, Boston, etc.

So, back to the original point - as  cities grow in size, they seem to become bluer (Democratic).  If these cities are in red (Republican) states, the state will trend to becoming purpler, and then blue.
Or, to put it differently, a Red state will remain red as long as it's cities do not become dense.
Or, to put it even more differently, low density suburban sprawl is a Republican ally...