Monday, May 22, 2006

Avoiding Gerrymandering

Gerrymandering is the practise of moving the boundaries of electoral districts with the aim of gaining an advantage in the results of a vote. The term gets its name from Elbridge Gerry, an American politician born in the 18th century who was involved in a notorious allocation of districts in Massachusetts in 1812. Gerrymandering reduces the effectiveness of a democracy by reducing the impact of each persons vote.

For example, if in a population of 50000, support for party A is 60% and support for party B is 40%, and this is spread randomly throughout 5 districts, it would be expected that party A would win 60% of the districts and get about 60% of the total vote. But if the districts are drawn up so that some districts contain a great deal more voters for party A than would be expected, say about 90% vote party A in two districts, this gives party B a majority in the remaining 3 districts, causing them to do better overall, despite not getting a greater share of the total vote.

Gerrymandering can also be used to make it harder for incumbent representitives to be replaced through similar tactics, this time by rearranging the district to remove those who may not be happy with the incumbents performance and politics.

There are a few simple guidelines for establishing the boudaries of districts that can greatly limit the ability of people to gerrymander.

1) The people setting the boudaries should be independent of elected representitives or political factions. If this is not possible, then a system by which all parties must agree to all new boundaries. In the USA, district boundaries are drawn up by the current legislature, and as a consequence, some districts are quite convoluted such as the 4th congressional district of Illinois.

2) The shapes of each district should be as simple as possible, while maintaining equal numbers of voters. Boundaries should be straight lines except when following natural features such as rivers or coasts, or where restricted by other causes (such as us congressional districts being in one state only). Ideally each district should be rectangular, or as close to as possible.

3) There are a few mathematical tricks and restrictions we can specify to prevent outragous districts. Set a maximum for the ratio of the square of the perimeter to the area of a district (For a circle this ratio is 4 pi, or about 12.57. Any other shape will have a higher ratio. A square will have a ratio of 16, a rectangle 4 times as long as it is high has a ratio of 100.

4) Get people out of the process all together. Computers can do all of this. We have a map, with people spread out all over it. We need to split it up into a certain number of divisions, and we want those divisions to have almost the same number of people in them. We also want the shape to be as simple geometrically as possible. This is exactly the sort of thing computers are good at. If someone were to put up a thousand dollar bounty and publicise it, this thing would be done in a week. Hell, I'm going to give it a go for myself once I find some useable population data.

These steps are all aimed at preventing people from setting district boundaries to suit their interests, because when that happens the value of a persons vote, and their say in the government is diminished.

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