Data Viz 101: Meet William Playfair
Welcome to Data Viz 101, Beutler Ink's introductory seminar on the wonderful world of data visualization. This course will cover all of the basic data viz concepts and best practices over a series of short blogs posts. And good news, class: there will be plenty of opportunities to learn, but no final exam.
Every introductory course should begin with history, and the history of data visualization begins with… well… it depends how you want to define data visualization. If by data viz mean simply mean visual representations of data, information, or even knowledge (which is effectively just accumulated data), then we could go all the way back to cave paintings which, historians now believe, depict a chronicle "log" of life from birth to death, with numerous celebrations and massacres in between.
But this is a boring, cover-your-bases answer. To see a real data visualization, we need to flash forward from crude cave paintings in Paleolithic Europe, past Sumerian script and Egyptian hieroglyphics (dyadic signifiers on your left), past Gerardus Mercator and history's forgotten cartographers (functional representation on your right), all the way to William Playfair, a Scottish engineer, inventor, and, well… , scoundrel with a showman's flare for visual presentation. Most of the charts used today in data visualization derive (at least in part) from Playfair's original designs.
Playfair's older brother—a professor of mathematics at Edinburgh University—inspired him to chart data over time and connect the dots. He put this approach to use in his 1788 work, The Commercial and Political Atlas, a compendium of bar and line charts representing imports, exports, wages, and other trends for different European countries. The publication is widely considered to be the first major work to contain statistical graphs.
In this example from the work, a line graph shows England and Scandinavia’s import-export balance for the 80-year span from 1700 until 1780. The balance of trade is the area between the two curves, which was shaded red when it was against England (prior to 1765), and green when it was in England’s favor. The shading actually turns this into an area graph.
And this graph from the Atlas's third edition shows England's then-soaring national debt. The chart starts at zero and extends to five hundred million pounds. The unused range at the top of the graphic subtly suggests that the debt rate will continue to grow in years to come. The graphic also uses an irregularly spaced grid along the time axis to demarcate events of significant economic consequence.
Playfair invented the statistical bar chart out of necessity, as he lacked the time-series data required to chart Scotland's imports and exports from and to 17 countries, so he instead used a form in which the horizontal axis did not represent the progression of time.
In Playfair's 1801 book The Statistical Breviary, he invented the pie chart from whole cloth to illustrate the Turkish Empire’s landholdings. The pie chart appears within a series of other circular charts, but this particular one is sliced into three slices whose sizes were determined by land area.
Like many researchers after him, Playfair understood the value of data visualization—that is allowed for easy and rapid comparison of a larger number of variables. Alas, Playfair's charts didn't catch on during his lifetime, and died in 1823 in poverty in relative obscurity. But gradually over the next century, the supply of readily available data grew, and bar, line, and pie charts became more common.
If you want to learn about William Playfair and his contributions to data visualization, we suggest this short but informative article from Ian Spence and Howard Wainer. And to prep for our next installment, we suggest checking out every book you can find about the Lady with the Lamp from your local library.