The graphs in this BBC article comparing several recent earthquakes hit us like aftershocks.
This chart tries to inform us the size of the quake in China was by far the largest. (The Richter scale is a power scale.)
The spirals feel like the Austin Powers time machine, disorienting, and also distracting because the bubble chart uses the entire area of the circles to represent magnitude. Try to guess what the relative amplitudes are before I disclose them below. (The red spiral for Italy was arbitrarily chosen as the index, with relative amplitude 1.) Bubbles are just horrible constructs, and for such a simple chart, they are worse than printing the data.
Amazingly, this is a double-axes bubble chart! The spirals hide the fact that the three gray circles are of different sizes, presumably color-coded to fit the "Strength" of the quakes. The other axis is "Relative Amplitude" represented by the red circles. Even though the two metrics are on hugely different scales, both the gray circles and the red spirals were anchored off the Italy red spiral (area = 1).
The following junkart version, which places the three quakes relative to the underlying relationship between strength and amplitude, is more informative with less fuss.
In the next chart, the Italians are shown to have no math skills (when in fact they have a strong tradition in math). How is it that 295 and 2000 have equal-sized bars? That's because the selected scale does not fit the data.
It's a mystery why Deaths and Injuries make friends while they ostracize the Homeless. The three series (deaths, injuries and homeless) can be displayed separately.
A simple data table, with appropriate highlighting, gets this information across without the confusion.
This next chart is decent. It is more effective if they make the Italy and Haiti blocks 20 across (same as the China blocks), stacking them one over the other. By doing so, the chart reduces to one dimension and we do not need to judge areas.
I think there is a calculation error with the Italy numbers. If 1 in every 190 affected died, then the number of affected is 190 x deaths, which from the above bar chart, equals 56,000. If only 56,000 were affected, how could 1.5 million be left homeless? (Wikipedia said 65,000 were made homeless.)
Overlapping non-concentric bubbles are also in need of rescue. Bubbles encode data in areas, areas are a square function of radii, the distance from the center to the circumference. When circles are not concentric, the centers do not coincide. This makes judging radii harder, which makes judging areas harder.
Look at Haiti vs. Italy. According to the printed data, the light gray area is about 60, which would be 40% of the dark gray circle. Who would have guessed? (I checked the areas, and indeed the Haiti area was 40% larger than the Italy area.)
By the way, in the first chart, the relative amplitudes were 40, 1 and 5. Who would have guessed?
Andrew Gelman recently talked about good graphics being hard. Graphs are easy to make but hard to perfect. These examples show the need for care.Reference: "Why did so many people die in Haiti's quake?", BBC News, 14 February, 2010.