The importance of a proper scale

Business Insider (link) highlighted a map showing childhood food insecurity across the 50 states, with the data coming from a report by Brookings.

This is a nice map. I like the tones of the chosen colors although the colors are not intuitively matched to magnitude. (There is a small labeling issue in the New England section.) The message is very clear.

*** I wondered about the scale, in particular, the use of equal sized buckets to split the scale. As a designer, several key decisions here include the number of buckets, and the size of each bucket. The following chart shows the choice made by this designer:

In this chart, all the states are ranked by their food insecurity rates with the lowest on the left and the highest on the right. The three horizontal lines show where the current cutoff values are. They form two equal sized blocks because of the equal spacing chosen by the designer. There are a total of four buckets.

Now if you ignore the dashed lines, and focus on the solid line showing the increasing food insecurity rates, you'd notice that maybe there are only three buckets, not four. The following amended chart shows where I'd put the cutoff values resulting in three buckets. (18% and 23%).

With the new cutoff values, let's look at what the map looks like:

I'm pretty happy with this. It shows an even clearer picture. There are three clusters of states, most of the south and west suffer more than the north and east. The odd state here and there (e.g. Louisiana) turned out not to be so special.

But this version picks out the "outliers", the group that has the best food insecurity rates than the rest of the country (as shown on the left side of the line charts). These particularly well-performing states are North Dakota and Minnesota, New Hampshire and Mass. and Viriginia.

A small shift in the scaling cleans up the message!

 

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Here is the same map with a progressive color scheme: