… identifying the political affiliation of parliamentary constituencies by colour on an ordinary, geographic map doesn’t quite work: not all constituencies are the same area, though each represents roughly the same number of people. As a result, expansive rural constituencies appear far larger than small but densely-populated urban ones. Thus, a geographic map appears very blue (for Conservative) because it over-emphasises rural constituencies. And Liberal-Democrats (in yellow) look as if they hold sway over one-fifth of the country, when in fact it is visually skewed by some big, sparsely-populated places. Labour's presence seems meagre.The Economist’s remedy:
… was an equal-area "Dorling" cartogram (below), named after Danny Dorling of the University of Sheffield. Part map, part graph, it let us depict every constituency at the same size, while keeping them in the approximate position and retaining the overall shape of the country. Because the variations in size of rural and urban constituencies are eliminated, the eye gets a far better sense of the actual distribution of political party representation.The Economist also:
added another layer of information: the strength of political support, by shade.
In the South West region however, the original geographic problem doesn’t really apply. There are only four urban Labour constituencies so the Lib Dem and Conservatives share the low density rural areas and the visual skew is small (detail below from the Daily Telegraph).
In fact the Dorling cartogram (detail above) introduces distortions of its own in the South West by putting Labour-held Exeter and Plymouth in adjacent hexagons while separating the two contiguous Bristol Labour seats.
The Economist didn’t state that the results they were presenting were for the 2010 election. If the Conservatives are to form a majority government after the 2015 election, as well as taking Labour seats in the North West and North East, they will have to take many of the 15 Lib Dem seats in the South West. My feeling is that the Tories will find that difficult and it will be interesting to see if the local elections next week support my view.