Tuesday 3 December 2019

Land doesn't vote, but it does matter

A short post today on the well-work topic of election mapping and, specifically, how to represent the results of elections in a way that reflects the true proportions of who voted for who. This isn't an attempt at a solution or a definitive answer, just some ideas and maps to provoke further thinking on the topic. Let's start by looking at two election maps (below). The one on the left colours in all constituencies according to the party of the MP at the end of the most recent UK parliamentary session. The one on the right is coloured in the same way but only where there are buildings. People like to use these kinds of maps with accompanying comments like 'land doesn't vote' or 'because sheep don't vote' (although I would like to see some polling on how they'd vote if they were so enfranchised). Scroll to the bottom to see the method for this in QGIS.

Standard map vs 'dasymetric' map
Some obvious stuff first... There's a lot of blue on the map to the left above. There is also quite a bit of yellow, and not much red. So, when we look at the map on the left it might give the impression of Tory dominance, when in fact they are not as far ahead as the colour share would suggest and  things are nowhere near as bad for Labour as it might appear from the colour share. Reasons include population density, urban voting patterns, etc, etc. But, but, but, when we get to this point, I always think "yes, true, but the vast majority of people know that". But then again maybe the vast majority of people have more exciting lives and don't think about this kind of stuff at all and end up being inadvertently misled my maps. Perhaps. SO, ENTER THE HEXAGON!!! Yes, it's our old friend, the hex map - example below from a new book. This definitely helps shift the story of the conventional election map from 'wow, the Tories are crushing the competition' to 'it looks quite close'. I quite like this approach, but with only a small quite and probably because of my own biases.

Hex for the win?

Yes, this hex map is better in many respects, but I'm not a huge fan of using these on their own and wouldn't really mind not seeing them again. But I do agree it provides a more useful representation of the vote share and as a compromise it's a fairly good one if we're interested in displaying vote share. I just think in this case a bar chart might be better if we're most interested in vote share, given how hard it is to get the hexagons arranged in a way that matches the underlying geography and what it does to my brain. That's why I've been experimenting recently with the dasymetric map style you see above. Talking of which, here are a few zoomed-in versions, with place labels, and a bit more discussion below.

What colour is your town?

This is a bit more informative I think

But I wouldn't use this approach on its own

Although I do think there is a place for this style

The colour balance is a bit more satisfying here

The last thing to say in this bit is that I also like the buildings-only maps with labels as it allows us to say a bit more about specific places. Let's imagine for a moment that there was a human being out there who didn't know the precise boundaries of the Berwickshire, Roxburgh and Selkirk constituency. I know it's hard to believe but I'm told such people do exist. They know it's a blue constituency and on the first map above they can actually see Selkirk (to the bottom right of the first labelled map) in blue, rather than a giant block of blue covering the entire area. 

Of course, this overlooks the fact that not everyone in the constituency voted for the Conservatives but that's another issue, and in a first-past-the-post electoral system I think shading by winning party is quite logical. Anyway, my point here is really that we can focus in on individual towns and how they voted without being distracted by giant wodges of colour that strictly speaking we do not need. I think the North of England map above does a good job of this - so you can just look at the east coast  of England and see that Bridlington or Scarborough are represented by the Conservatives and that Blackpool has a red wedge between two blue blobs on the west coast.

If you did want to colour areas by the strength of vote for one party then you could use what I call a 'staunchmap' approach, like the example below that I've shared previously. The deeper the colour the higher the vote share - e.g. see Merseyside and its deep Labour reds.

Who will win in 2019? I predict nobody will win.

So, what's my final verdict on how best to map elections? I think a mix of approaches is best, and because most of what we view is on multi-media platforms I think some use of animation might be useful, as in the gif I made already and shared on Twitter. In print or static format this could just be a simple side-by-side version, like the image at the top of the page. Actually, having just written this, I think broadcasters and print media should do both - perhaps standard map + hex + dasymetric or standard map + one other. Not that it matters that much but if we've got the data and tools seems like it would be a good idea to use them here and, maybe, pass on a little more information with this slightly different encoding.

Ooh, fancy - but it does add a bit of value I think

("land doesn't vote, but it does matter" is my usual thought on this, so I'm adding it here, and that's why I'm using a technique that does at least show the land at some point, before switching to a view that more closely reflects the numbers we're probably interested in. Plus, we can't have the Highlands zapped from the map, or at least not permanently.)

Data and method: a cumbersome way to do this would be to use a buildings layer to clip the constituencies but that would take ages. I did this in QGIS using a simple blend mode but it's possible with other tools as well. The data I used are from the spreadsheet I put together and shared on Github previously. You'll also find a constituencies file there to to join it to. You can grab the buildings layer from this page and then you've got all you need to replicate what you see here. Just take a look at the screenshots below to see how I did it. Just make sure your map canvas background is black (via Project > Properties > General).

This is the layer order you need

The constituency colours come from the attribute table

The buildings are all white, with a thin outline