Monday, October 25, 2010

Everything You Ever Wanted To Know About Gerrymandering

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What the Deuce is Gerrymandering?
Gerrymandering is the practice of carving up representative districts in a…creative fashion to benefit one party or another. The early ideal for carving up our new nation into representative districts was relative compactness. In 1812 Elbridge Gerry (sounds like “jerry”), governor of Massachusetts, carved up his state into curious districts that would benefit his party, causing political commentators of the time to lampoon the districting as looking like a salamander. The Boston Gazette ran a cartoon of the "Gerrymander" and the rest is history. By the way, this original gerrymander seems to me pretty tame compared to some you are likely to see today.

The first "Gerrymander." Suspiciously-political districting drew the ire of the Boston Gazette, who published this cartoon.

Who Benefits from Gerrymandering?
The sticky wicket of districting is, like history, the folks in charge get to decide. It is impossible to realistically separate the drawing of districts from political advantage, which, realistically, gets banged out during an over-nighter locked-door wheel-and-deal session probably devoid of even the idea of math.
There is no consistent gotcha finger you can point at a gerrymandered district, however. Sometimes the guy twisting his long waxy mustache is the party that lost that district. Why? Because often the strategy is to pack in a supermajority of opposition voters into one district and write that off as a guaranteed loss, but then be assured to win the surrounding districts.
Other times the benefit falls to the winner of the gerrymandered district that encompasses a minority enclave, which, otherwise, would not have “their own” representation in congress.
Wikipedia has a great section on the various possible goals and benefactors of a gerrymandered district in an authoritative tone that I can't hope to equal.

The Gerrymander Mojo Index.  An alright first step at ferreting out Gerrymandered districts.  Alaska and Hawaii aren't included, and you aren't missing much: the complexity of their coastlines ruins the usefulness of this index (see the "Caveats" section below).

Why is Gerrymandering Important to Understand?
The United States is a representative republic…not a pure democracy. Each voter does not vote on each bill. Instead, we vote on representatives who act as our proxy in congress. How do we lump ourselves up for representation? Districts. Districts! So, geography is one of the single biggest factors driving our representative republic. And, considering how important districting is, the rules for defining them are pretty loosey goosey.
So let’s use extremes as examples, as that’s a pretty helpful tool for illustration in this case. Suppose folks in the United States are the product of an absolute melting pot; where we live doesn’t have much to do with how we think, and in turn how we might vote. In this case divvying up people into geographic districts is a simple task of finding the most evenly populated compact voronoi shapes, and think nothing else of it. Alternatively, consider the United States as a conglomerate of segregated socio-economic-politico-ethnic camps who vie for representative leverage. Drawing representative districts then becomes primarily a political (rather than geometric) task and the resulting territories may be impossibly undulating and complex in an effort to grab even populations of “like minded” folks.
The reality is somewhere in-between. And my sense is that wherever your notion of relative American mixedness (in reality and idealistically) falls within that spectrum will pretty well predict your relative comfort with gerrymandering. So you can take that for whatever it’s worth.

Our Gerrymander Mojo Rating... the perimeter divided by the square root of the area.  The ratio of perimeter to area will give you a good idea of the relative splatteredness of a shape.  And, taking the square root of the area will ensure that the ratio is consistent at all scales (so large districts aren't biased towards compactness).  If something is nice and compact (like a circle or...Wyoming), the result is a small number.  If something is hopelessly undulating (like Illinois' 4th congressional district), the number will be large.  A rough index like this is a good starting point for looking into potential Gerrymanders, and might lead to some interesting questions.

Two predominantly Hispanic neighborhoods on either side of Chicago, linked by a precarious stretch of Interstate 294, form the interesting 4th Congressional District of Illinois.

The state of Wyoming (which is, in it's entirety, a single congressional district) can't believe how compact it is.

Wait a second, what makes relatively compact shapes so special? Even if you consider the population of the U.S. as wholly mixed and you reject boundaries characterized by ethnicity and wealth and so on, you still have to admit that the patterns of our nation’s development (and the patterns of human settlement in general) are complex and meandering in shape and influence and awkward squiggly groupings thereof are more accurate delineations than arbitrary compact cookie cutter shapes. What’s more, the complex geographic landscape that we settle into (like meandering rivers and valleys) certainly isn’t characterized by highly efficient shapes of elegant compactness.
What I mean to say is that coming up with an ideal district shape philosophy is hard, and lots of factors go into the forming of a district that are not necessarily nefarious or even political in nature (but...come on).  Districts that skirt rivers or coastlines, or straddle mountain ranges will wreak havoc on our simple index of Gerrymandering; keep this in mind as you browse our maps.  In short, ratings like ours should be taken with a grain of salt.

Some Interesting Districts (other than the two up there)...
Illinois has more than one intriguing district.  Like it's cousin, the 4th, the 17th district is a clear recipient of political maneuvering and has been nicknamed the "Rabbit on a Skateboard."

California's 23rd district encompasses a very thin stretch of much of California's southern coast.

The Wall Street Journal called North Carolina's relatively new district (1990) "political pornography." This district led to a Supreme Court case over gerrymandering in 1993.  You can't make this stuff up.

Florida's 22nd district has fingers that meander into several cities.  This district was at the center of the 2000 Presidential Election recount.

The districts surrounding Maryland's 3rd district can be forgiven because their complex coastlines blow out our index.  But that 3rd District got cranked right out of the gerrymander factory.

New Jersey's 6th district's already interesting shape generates additional interest with the inclusion of a lobe connected by a thin stretch of beach.

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  1. Got some time on your hands since the v5 release?

    Great post John!

  2. Very interesting and even a little disturbing. Haven't we evolved enough as a country to be better than this?

    Good writeup though. Well done-

  3. This is not up to date with the latest Ohio debacle. Look at the Ohio 16th and 7th on the new map (not on the one you are using in this post). Ridiculous.

  4. Thanks Unknown, We'll all Google it.

  5. California's districts were created by a bipartisan (tripartisan? -- members were Democrats, Republicans, and independents) citizens commission and not by the state legislature. Much of the complexity of the 23rd district derives from its alignment with the coast. The people of the 23rd have a great deal in common, all living on or in close proximity to California's south-central Pacific coast. Although it crosses several county boundaries, the 23rd is based on a solid rationale for a community of mutual interest. It doesn't make a particularly good example of gerrymandering.