Jon P took my comment on negative correlation and explored it further. Given the large ranges of values cited in
the original Economist chart, Jon concluded that there wasn't enough
evidence to make a judgement.
I agree to a large extent. Apart from the high variability of individual measurements, we also face the tiny sample of 5 cities. In his chart, he made an implicit assumption that the correlation of two factors is related to the product of the ranges (variability) of each factor by plotting the rectangles.
A different way of looking at it is to plot only the mid-range values (i.e. ignoring the within-city variability). The graph on the left hand side shows very little pattern.
Resorting to the formula, I found that the correlation = -0.03. So barely detectable negative correlation. Lets visualize this.
On the right graph, I added the mean lines for both variables. This divides the graph into four quadrants; dots that fall into the lower right and upper left quadrants make the correlation value negative. There were three of those versus two in the positive quadrants; hence, the tiny negative correlation.