Friday, February 13, 2015

Voting Districts and Gerrymandering



Super idealized city





Capture ALL the cities!
And my personal favorite:





  • Canada: 1.400
  • USA: 2.103
From the report, the historical comparisons look like this:

Hill, 2009





Saskatchewan was solid (average: 1.31)
Newfoundland and Labrador averaged 1.52, because shores are tricky




Paul said...

Compactness is definitely desirable for any voting district but keep in mind that compact configurations can still be used to dilute certain voting demographics and favour certain parties. The case has been seen in many 'rurban' districts in Saskatchewan and Alberta prior to this year's reconfiguration. Some have protested the new alignments claiming that it would initiate an urban and rural divide.

That said, wouldn't it be interesting to see proportional representation occur in our lifetime?

Richard said...

I'd be interested to see that Alberta map superimposed with a poll of where people usually vote, because the conservative party has been accused of gerrymandering. I agree with Paul, I'd much rather see proportional representation than keep status quo with our electoral system.

Anonymous said...

The 'compactness' will surely be related to the local population density, as size of the voting districts will be inversely proportional with this metric, and necessity of making very sharp cuts through the geography will be diminished. As the population density of the US (even including Alaska) is nearly an order of magnitude higher than that of Canada, it should be expected that the 'compactness' will be higher in the US. I'd imagine that if the 'compactness' to population density of all of the voting districts were plotted, you'd see a strong correlation - something to look into.

Additionally, the term 'compactness' is a poor choice, since larger 'compactness' means it is in fact less compact, so the term should by diffuseness or something similar.

The choice of definition of the metric used is also poor, as something that is very compact, but has surface roughness could rate as high as a region which is actually what you want to define as not ideal. Indeed, you concede that regions like Labrador, which are along coastline, will surely have a large perimeter length even though they are close to being as compact as it can be. A better way would be to divide the area of the voting district by the area of the convex hull. In this case, a compactness of 1 still signifies the ideal square situation (and indeed any convex shape like a circle or rectangle), and lower values are less ideal. The area of the convex hull can also be altered to discount any regions cutting over water, eliminating the issue of coastline. If you wanted to penalize elongated but convex districts, you incorporate the aspect ratio of the convex hull as an additional factor, but I find the thing that people recognize most abhorrent about gerrymandering is the exaggerated concavity of polygons used to bound districts.

Now, you may still find that Canadians are more honest and less prone to gerrymandering than Americans, but I feel like this alternate method would show this with more confidence.

Anonymous said...

Very interesting article, however your data is off by a few years. California was redistricted in 2012 using a bipartisan commission with data from the 2010 census. This resulted in more competitive districts and a top-two blanket primary. The districts you showed are prime examples of how gerrymandering was out of control in the state. If you look at the districts now, you can see more cohesive, contiguous areas.

Mapleson said...

I think two things could be done to improve this analysis. First would be to give ridings that run along physical/provincial boundaries a lower weighting (could part of the difference between Canada and the US be that Canada has more regularly shaped provinces?). Second, a comparison to population density per riding. Ideally, a riding would not be 90% rural and 10% urban (like the two for Alberta that split up Fort MacMurray).

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