In past years, a common feature of CHIFOO programs was the request for someone in the audience to act as a journalist for the evening, and write down their take on the presentation. It allowed us to hear (or, rather, read) different viewpoints, and also provided an unbiased view of the proceedings for the presenters and organizers (so that we would know if our efforts were hitting the mark). It also provided a valuable record of the evening as it actually happened (rather than how we planned for it to happen), helping to add color to the program description and the presenter’s slides, and to improve the quality of our web site archives as a resource for the CHIFOO community—and the world.

We’d like to continue this tradition. With the Comments section of our… READ MORE »

This is certainly not an exhaustive review of the topic. There are many kinds of visualizations I won’t be able to explore in a blog post. The common thread here is simply “things I’ve found while researching another project I’m working on for my information visualization class.”

Nightengale’s Coxcomb

One of the earliest examples is Nightengale’s Coxcomb. This graph was created by Florence Nightengale during the Crimean War to advocate for better sanitation. It shows that the number of deaths due to preventable causes (blue wedges) exceeds the number of deaths due to wounds (red) and other causes (gray). It also shows the success of sanitation efforts – the decrease in preventable deaths in April 1855 corresponds to sanitation cleanup efforts in Turkey.

Figure 1: Nightengale’s Coxcomb

The major advantage of the circular layout of the coxcomb is the way months have a consistent placement around the axis. This makes it easier to do year-on-year comparisons. (This will be a recurring theme.)

Nightengale was careful to map data values to the area of wedges, not the radius. This solved one problem, but introduced another. Nightengale was avoiding the problem where area increases as the square of radius. Had she mapped her data values to the radius, this would have exaggerated the values, since a doubling of the radius would show a quadrupling of the area (Rehmeyr, 2009). But by avoiding that lie factor, Nightengale made it somewhat harder to compare months. You can somewhat easily tell that the radius for January 1855 is about twice as long as the radius of November 1854. But what of the area? People aren’t that good at estimating area, especially of odd shapes like wedges (or even rectangles with differing aspect ratios).

Teoria Generale Della Statistica

Figure 2 avoids the area/radius confusion of Nightengale’s coxcomb, by plotting the data as spokes on a wheel. It is also much less visually striking than the coxcomb. It’s okay, sometimes, to sacrifice some utility (but not honesty) to increase impact.

Figure 2: An early circular plot (Gabaglio, 1888)

The graph comes from Teoria...