Graphs are essentially images that are used to convey information in a more simplistic, and typically easier to understand manner. The use of comparative design, where you take a familiar or recognizable artifact (i.e. a circle) and then apply the information to that artifact (thusly creating a pie chart) is an incredibly useful means of translating statistical information into a visual genre. Another example would be using bar graphs to convey information that may not equal up to a whole (100%) like it would with a pie chart, but still allows you to compare statistics visually.
Enter the Nightingale Graph. The first instance of this graph circular graph was developed by its namesake, Florence Nightingale to illustrate the number, and means of deaths in the field hospital she worked in during the Crimean War. Essentially what the graph is, is a multi-layered bar graph wrapped into a circle to emulate the cyclical nature of the calendar. There are many issues with this graph, such as no indication of number, the “fanning out” of the representational areas could distort the amount of information, and in today’s culture, when people see circles they are most likely to be looking for percentages .
While the Nightingale Graph is certainly useful in some respects, it is antiquated and very counterintuitive to look at it, not to mention there is no frame of reference for its statistical accuracy.
Good analysis here, but just because you find the Nightendale graph to be antiquated, it doesn’t mean that is doesn’t still tell us something about visual rhetoric.