The simple explanation for this is that nearly two thirds of voters the seventh district are African American, a group that overwhelmingly supported Jones in his contest with Roy Moore.
The 7th District is in fact home to nearly one-third of the state's entire black population. Having so many black voters in the 7th District means there are fewer black voters everywhere else.
There's no such skew in the distribution of white voters across the state's districts: White voters are distributed evenly pretty much everywhere, with the exception of the 7th District.
This is no accident: The state's Republican lawmakers drew the district boundaries following the 2010 Census, as required by the Constitution. Let's take a look at those district boundaries, overlaid on a map of the black population at the Census block group level. Pay particular attention to the borders of the 7th District.
The 7th District encompasses most of the western portion of Alabama's “black belt,” a region of the state with a historically large black population. But it also has a number of conspicuous appendages that poke into neighboring areas: One snakes down into the 1st District, picking up a large chunk of the black population around Monroeville. Another extends into the predominantly African American neighborhoods in west Montgomery.
Most striking is the narrow arm that runs through Tuscaloosa straight through the heart of Birmingham, picking up many of the majority-black neighborhoods in those cities along the way. The net effect is to remove a large number of black voters that might otherwise have been part of the 4th and 6th Districts.
The population of black voters in the eastern portion of the state, meanwhile, is split neatly in two by the border between the 2nd and 3rd Districts.
All told, the district boundaries ensure that while black voters have a sizable majority in district 7, their power is diluted everywhere else in the state. There's a word for this: gerrymandering. It refers to the process of drawing district boundaries in a way that makes it easier for you to win elections.
Earlier this year a federal court ruled Alabama Republicans had improperly gerrymandered districts for the state legislature, packing black voters into a small number of districts to dilute their power elsewhere.
The legislative boundaries for Alabama's U.S. House districts weren't part of that lawsuit, but the lopsidedness of the distribution of black voters across those districts is strikingly similar.
Part of this may be due to the Voting Rights Act, which makes the drawing of districts in this fashion permissible and even required in many cases. To ensure minority voters had at least some representation in Congress, the act required the creation of some majority-minority districts.
But as Wonkblog detailed earlier this year, “majority-minority districts, by concentrating the minority vote in certain districts, have the unintended consequence of diluting their influence elsewhere.” In recent years Republicans in a number of states have taken advantage of this, drawing favorable electoral maps in the ostensible interest of minority representation.
The Supreme Court has shown renewed interest in gerrymandering cases this term, taking up lawsuits against Democrat-drawn districts in Maryland and Republican-drawn districts in Wisconsin. The outcome of those cases could severely limit the ability of lawmakers to gerrymander their way into power.
Regardless, experts who study gerrymandering say it will continue to be a problem as long as partisan lawmakers are able to draw their own districts, rather than letting independent commissions (or even computer programs) do the work.
In 42 states, including Alabama, politicians are in charge of redrawing legislative districts.