Three colour mixing of 129,211 census enumeration districts smoothed by ten passes of a binomial filter on an equal population cartogram — software by author on an Archimedes computer.
Here the image is, perhaps, made clearer by smoothing. In places the blue and yellow colours have run into each other and produced a green which does not reflect reality. In central London the algorithm has failed along the cliff between the most and least prosperous places, so here it is shown as a white ring around a blue core. The filter works best where the underlying pattern is most amenable to being smoothed.