In Florida, as is common around the country, Democrats are highly concentrated in urban centers like Miami; Republicans are more spread out around the state. This means residents of Democratic-leaning precincts are far more likely to have similarly voting neighbors than red-leaning precincts are. And since Florida’s congressional districts must by law be contiguous and compact, Democrats are more likely to be packed into districts that are overwhelmingly Democratic than Republicans are. Nate Cohn, my colleague at The Upshot, has written about the phenomenon of “wasted votes” and how it hurts Democrats in states like Pennsylvania.

In Florida, unlike in most other states, this Democratic concentration is so extreme that even in partisan-blind districts drawn by a computer, the Republican bias remains. In Mr. Chen and Mr. Rodden’s simulations, they found that when the Florida vote was slightly tilted toward Democrats, as it was in the 2008 presidential election data they used, Republicans would still win 52 to 56 percent of the House seats, on average. These simulations notably held Florida’s three majority-black districts, one of which was struck down as a partisan gerrymander, constant, forming the other 24 districts out of the remaining precincts.