I read recently this article on the BBC News website. I thought the map they used (below) to show the areas of Britain with the largest domestic carbon footprints was a little uninspiring.
The colour scale was unclear with no explanation as to why the numbers jump around (the interval changes from 1 to 2) and appears to, for example, ignore the values that fall between 24 to 26 tonnes per household. Southern England is too red in the sense that it is hard to distinguish between areas with the highest emissions. I also feel that a more useful variable to plot is whether areas are increasing or decreasing their domestic carbon emissions. I understand why people are keen to highlight, for example, that David Cameron’s constituency is one of the top 40 most polluting, but it presents a static picture. It may be that he has heavily invested in household energy efficiency programs and dramatically reduced emissions compared to a few years ago- equally the constituency’s emissions could be increasing because he has avoided potentially unpopular environmental policies.
In response to my comments above I have logged on to the Guardian Data Blog to get hold of the UK Carbon Emissions by Local Authority Data they have published. In order to represent both total emissions and improvement between 2005 and 2007 I have opted to use cartograms. The first cartogram focusses on the Local Authority (LA) by rescaling their boundaries by the total domestic carbon emissions. The colours represent the % reduction or increase in emissions between 2005 and 2007. So areas that have been expanded a lot and coloured red are large domestic emitters and getting worse, whereas shrunken blue areas are already low domestic emitters that are reducing emissions. I have used Jenks’ Natural Breaks to decide the transitions from one colour to the next.
This second cartogram is subtly different because the boundaries are scaled by the average per captia emissions for each LA. An enlarged area is one where the people living there are relatively high emitters of carbon dioxide. Their total contribution from the entire LA population (as shown in the cartogram above) can still however be small compared to other areas in the country. Equally a large LA can appear as a large emitter in the above map simply because more people live there even though they may have very low per capita emissions as shown below. As before the colours represent the % increase or decrease in carbon emissions between 2005 and 2007. I don’t think these maps are perfect by any means but they present a more eye-catching interpretation of an important but heavily discussed issue.