Category Archives: Automated Redistricting

Checking District Contiguity

Though not a federal standard, contiguity is the most common state-applied standard for district maps, and therefore is an important feature to be able to guarantee in any automated redistricting program. Put simply, one should be able to walk from any point in the district to any other point in the district without having to cross a district boundary.

Contiguity checks can be useful in other contexts, too. For example, when examining the changes made between a proposed district plan and its amended version in the redistricting process, it is relatively simple to generate statistics on, say, the people who were moved out of a particular district. But it’s possible that two different chunks of people were moved out, from opposite ends of the district and with different demographic profiles, or perhaps more than a dozen different chunks (see: changes to congressional district 5 in the Florida redistricting process). Sorting out the different groups can be done visually with a program like ArcGIS, but if you’re doing this process on a number of different districts in a number of different maps, it’d be nice to have an algorithm to separate out the pieces for you.

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Automated Redistricting and the Florida State Senate

The latest challenge of Florida’s congressional districts wrapped up last week, which brought to light a lot of questionable behind-the-scenes behavior on the part of the Florida legislative leadership during the redistricting process. Should the ruling go in favor of the Democrats and the League of Women Voters/Common Cause coalition, the findings produced during the case make it likely that the state senate maps will be challenged (again) afterward.

It’s easy to get cynical about the process, no matter what supposed safeguards are in place, such as Florida’s 2010 “Fair Districts” constitutional amendments. Many come to the same conclusion as Christopher Ingraham at the Washington Post – why not consider letting computers do it?

Like Ingraham says, algorithms for redistricting already exist, and have for over fifty years now. The operations research literature has had quite a bit of discussion on potential methodologies, as have election law journals and random programmers, ranging in levels of sophistication and computational complexity. There are a couple algorithms in particular I seem to see posted regularly around online. They’re both great in what they set out to achieve, and have made some headway in popularizing the idea of automated redistricting, so I’m a fan of the creators of both. Unfortunately, both algorithms fall on the simplistic side of suggested methods (by design), which has some major drawbacks.

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