Algorithmic Redistricting and Range Voting

Posted in politics at 12:32 pm by danvk

Computer algorithms are an appealing way to fight the problem of Gerrymandering, since they’re independent of politics. I had a great time this morning reading about one such algorithm for redistricting at rangevoting.org.

Here’s a map of Arizona’s eight congressional districts as determined by their statehouse (left) and the algorithm (right):

Arizona's congressional districts from 2002Arizona's congressional districts, as determined by the splitline algorithm

Check out Arizona’s second congressional district!

The splitline algorithm is quite simple. You find the shortest line which splits the state’s population in half. Then find the shortest splitlines in those halves, until you have enough districts. The exact details are here.

I like the simplicity of this approach, but I think there’s some benefit to having coherent districts, i.e. a community having their own representative instead of being split between two representatives of other communities. That being said, I don’t see much evidence that legislatures do this right now, and it seems like a hard thing to incorporate into an algorithm. The splitline approach certainly seems better than the status quo!

I also enjoyed their discussion of Range Voting, a generalization of Approval Voting (Approval Voting is a system in which you say whether you’re OK with each candidate, rather than picking a single one).

In Range Voting, you give each candidate a rating from 0-10, or maybe 0-100. The candidate with the highest average rating wins. By letting you consider each candidate independently (instead of choosing just one or ranking them), it avoids some of the pitfalls inherent in preferential voting systems. And it has more appeal than Approval Voting because it’s more expressive: I can say that I like candidate A more than candidate B (who I’m just OK with), rather than just saying that I approve of both. Even mother nature likes range voting: Honeybees have evolved a form of it!

One interesting thought: if a state switched to using range voting or instant runoff voting, how would it affect the National Popular Vote Bill? Can we have both?

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