Seven years ago, I wrote a post about "invariance" in data visualization, which is something we should avoid (link). Yesterday, Business Insider published the following chart in an article about rising gas prices (link):
The map shows the average prices at the pump in seven regions of the United States.
This chart is succeeded by the following map:
This second map shows the change in average gas prices in the same seven regions.
This design is invariant to the data! While the data change, the visualization looks identical. That's because the data are not encoded to any visual element - they are just printed as labels.