What do we want to learn about gas prices this summer?
Which region has the highest / lowest prices?
How much higher / lower than the national average are the regional prices?
How much has prices risen, compared to last year, or compared to the last few weeks?
How much work did you have to do to get answers to those questions from the above map?
Unfortunately, this type of map continues to dominate the popular press. It merely delivers a geography lesson and not much else. Its dominant feature tells readers how to classify the 50 states into regions. Its color encodes no data.
Not surprisingly, this map fails the self-sufficiency test (link). The entire dataset is printed on the map, and if those numbers were removed, we would be left with a map of the regions of the U.S. The graphical elements of the chart are not doing much work.
In the following chart, I used the map as a color legend. Also, an additional plot shows each region's price level against the national average.
One can certainly ditch the map altogether, which makes having seven colors unnecessary. To address other questions, just stack on other charts, for example, showing the price increase versus last year.
From a Trifecta Checkup perspective, we find that the trouble starts with the Q corner. There are several important questions not addressed by the graphic. In the D corner, no context is provided to interpret the data. Are these prices abnormal? How do they compare to the national average or to a year ago? In the V corner, the chart takes too much effort to comprehend a basic fact, such as which region has the highest average price.
For more on the Trifecta Checkup, see this guide.