Here's a beauty by WSJ Graphics:
The article is here.
This data graphic illustrates the power of the visual medium. The underlying dataset is complex: power production by type of source by state by month by year. That's more than 90,000 numbers. They all reside on this graphic.
Readers amazingly make sense of all these numbers without much effort.
It starts with the summary chart on top.
The designer made decisions. The data are presented in relative terms, as proportion of total power production. Only the first and last years are labeled, thus drawing our attention to the long-term trend. The order of the color blocks is carefully selected so that the cleaner sources are listed at the top and the dirtier sources at the bottom. The order of the legend labels mirrors the color blocks in the area chart.
It takes only a few seconds to learn that U.S. power production has largely shifted away from coal with most of it substituted by natural gas. Other than wind, the green sources of power have not gained much ground during these years - in a relative sense.
This summary chart serves as a reading guide for the rest of the chart, which is a tile map of all fifty states. Embedded in the tile map is a small-multiples arrangement.
The map offers multiple avenues for exploration.
Some readers may look at specific states. For example, California.
Currently, about half of the power production in California come from natural gas. Notably, there is no coal at all in any of these years. In addition to wind, solar energy has also gained. All of these insights come without the need for any labels or gridlines!
Browsing around California, readers find different patterns in other Western states like Oregon and Washington.
Hydroelectric energy is the dominant source in those two states, with wind gradually taking share.
At this point, readers realize that the summary chart up top hides remarkable state-level variations.
There are other paths through the map.
Some readers may scan the whole map, seeking patterns that pop out.
One such pattern is the cluster of states that use coal. In most of these states, the proportion of coal has declined.
Yet another path exists for those interested in specific sources of power.
For example, the trend in nuclear power usage is easily followed by tracking the purple. South Carolina, Illinois and New Hampshire are three states that rely on nuclear for more than half of its power.
I wonder what happened in Vermont about 8 years ago.
The chart says they renounced nuclear energy. Here is some history. This one-time event caused a disruption in the time series, unique on the entire map.
This work is wonderful. Enjoy it!