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The Graphic Truth

We have all been taught to be critical of the written word, but we tend to let the omnipresent graphics of our era pass without close scrutiny. This we do at our own loss and peril. Graphics are rich stores of information, but often they lie about quantitative information and are unnerving and confusing when they could be aesthetically pleasing. In his recent book, The Visual Display of Quantitative Information, Edward R. Tufte tells us what we should treasure, reject, and censor in graphics—and much more. It is a thoroughly engaging and handsome volume that should inform and entertain everyone from scientists and engineers to economists, as well as every kind of historian.

 

The book deals with the design of statistical graphics—a formidable subject until Tufte shows us that it is “often the most effective way to describe, explore, and summarize a set of numbers” and that it is, in fact, a device for looking “at pictures of these numbers.” Tufte is well qualified to write this elegant and thoughtful introduction to the subject—he is a professor of political science and statistics at Yale University, a consultant on graphics for the media, and also the founder of Graphics Press, of Cheshire, Connecticut, which published the book.

 

Showing numbers with abstract, nonrepresentational pictures is, Tufte informs us, a surprisingly recent invention. J. H. Lambert (1728–77), a Swiss-German scientist and mathematician for whom the “lambert” unit for measuring the brightness of light is named, and William Playfair (1759–1823), an English political economist, were prominent among the innovators. Playfair’s imaginative and craftsmanlike graphics have stood the test of time so well that Tufte uses them to make points about good contemporary graphics design. Playfair’s The Commercial and Political Atlas (London, 1786) has forty-four charts, all but one of which are time series that show, for instance, imports and exports and the balance of trade in England over almost a century. The one exception is the first known bar chart, which he invented to portray one-year data.

 

Tufte illustrates with classic graphics, some of which dramatically and deftly convey the essence of momentous historical events. With brutal eloquence, Charles Joseph Minard (1781–1870), a French engineer, shows the tragic course of the invasion of Russia by Napoleon’s army from 1812 to 1813. Minard extends across Russia a band diminishing in width as it approaches Moscow and shrinking to a thin line as it retreats to Poland. The full width represents the invading army (422,000) and the pathetically thin one the remnant straggling into Poland (10,000). This multivariate graphic plots army size and location on a map, direction of movement over time, and the temperature on various dates during the deadly winter of retreat. Tufte comments that “it may well be the best statistical graphic ever drawn.”

 

A superb diagram by E. J. Marey (1830 – 1904) also exemplifies the clear visual presentation of complex relationships. Marey shows graphically a schedule for Paris-to-Lyon trains in the 1880s. The intervening train stations are named along the vertical axis and separated by intervals proportional to the actual distance between them. The horizontal marks the twenty-four hours. The slope of the lines that represent the various trains gives, therefore, the speed of the trains—the steeper the slope, the faster the train. (A vertical line would mean velocity at the speed of light, an achievement still eluding even the new Paris-to-Lyon express.) The intersection of upward lines with the downward gives the time when Paris-to-Lyon trains meet those heading for Paris. Every railroad buff should have the Marey graph among his collection of schedules.

 

There are other gems. Dr. John Snow used dots on a map of London to locate cholera deaths in London for September 1854. He also showed water pumps. From the plot emerged a pattern of deaths around the Broad Street water pump; when the handle of that pump was removed, the neighborhood epidemic that had taken more than five hundred lives ended. Some historians still use statistical graphics in the detective work of finding pattern and cause in history—graphs often provide clues that a detailed narrative can investigate and explicate. For instance, Alfred D. Chandler, Jr., the doyen of business historians, saw a pattern of revolutionary industrial development in a time-series plot of iron and anthracite-coal production in northeastern Pennsylvania during the middle decades of the nineteenth century. Driven by the scent of truth, he then wrote a seminal article, in 1971, to document and narrate the Industrial Revolution in America. Fernand Braudel, the distinguished representative of the Annales school of French historians, employed no fewer than sixty-eight figures in his two-volume history of the Mediterranean, most of which are ingenious visual displays of quantitative information. It is notable that reviewers of these highly praised volumes rarely mention the role graphics play in the Braudel style.