Monday, June 14, 2021

Gerrymandering in London

The Boundary Commission for England recently released its 2023 Review of Parliamentary Constituencies. This review includes its proposals for how parliamentary constituencies in England (Scotland and Wales have their own boundary commissions). The Boundary Commission's Find Your Constituency tool allows you to view the new recommended constituency boundaries on an interactive map and compare the new boundaries with the existing constituency boundaries.

If you live in England you can use this new tool to view if and how your local constituency boundary (which is represented by your local Member of Parliament) would change under the commission's recommendations. You can also use the map during the consultation process to submit your response to these proposals. 

As you can see from the image above my new constituency of West Ham & Beckton is a very odd shape.Being something of a map nerd I decided to explore how the proposed changes to my local constituency scores on the Polsby-Popper test. 

The Polsby-Popper test is a mathematical formula for calculating how compact an electoral district is in order to detect for possible gerrymandering. The general assumption is that the more an electoral district veers from being compact then the more likely it is to have been gerrymandered.

Explained simply a Polsby-Popper score is the ratio of the area of an electoral district to the area of a circle whose circumference is equal to the perimeter of the district. The proposed new constituency boundaries for London are available for download here. I was therefore able to download the new London boundary geographies as a KML file. I then used the MyGeoData Convertor to convert the data into the GeoJSON format.

The data from the Boundary Commission for England includes the area of each new electoral district. To work out the perimeter of the district I used turf.js with my GeoJSON data. With both the area and perimeter length we can then work out the Polsby-Popper Score.

The West Ham & Becton Polsby-Popper score is: 0.40940602755

A Polsby-Popper score always falls within the range of 0-1, where 0 is least compact and 1 is most compact. A score of 0.40940602755 is closer to 0 than to 1 so this suggests that the new proposed constituency boundary for West Ham & Becton is not very compact.

Despite its very odd shape and the fact that it is not very compact I don't believe that the new proposed boundary for my constituency has been gerrymandered. The Boundary Commission for England is an independent body and I really don't believe that they have any interest in gerrymandering electoral districts in favor of any of the UK political parties. However West Ham and Becton's Polsby-Popper score does suggest that at least in East London the commission has struggled to create logical new constituency boundaries. 

The existing constituencies. Under the new proposals a large area of East Ham will become part of West Ham & Becton

One of the main requirements for the new boundaries is that a constituency must have a population between 69,724 and 77,062. However the commission also considers 'local ties, geographic factors, local government boundaries ..., ), existing constituencies, and minimising disruption caused by proposed change'. In West Ham & Beckton it seems that the struggle to create a constituency with the correct population means that other factors have been to some extent overlooked.The result is that a large area which has been historically represented by the East Ham Member of Parliament will now be represented by the West Ham & Becton MP.

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