William Playfair - a businessman, engineer and economics writer from Scotland - created the first known pie chart in 1801. Seeking to illustrate the Turkish Empire's landholdings for his statistical breviary on the European nation-states, Playfair sliced a circle into three wedges whose sizes were determined by land area. According to a paper called No Humble Pie: The Origins and Usage of a Statistical Chart by Ian Spence, professor of psychology at the University of Toronto, Asia's wedge was the largest and coloured green, to indicate that it was a maritime power. Europe was made red to indicate it was a "land power". It's not clear why Playfair made Africa yellow, or what inspired him to make a circle graph at all. But, Spence writes, it was "the first pie chart to display empirical proportions and to differentiate the component parts by colour".

By midcentury, the pie chart was growing in popularity. One of its first champions was Charles Joseph Minard, an engineer who once used a flow map to depict the casualties Napoleon's army suffered during the Russian campaign. In France, the pie chart became known as le camembert, because of the way a wheel of cheese is typically divided. Florence Nightingale drove home the impact of poor sanitary conditions on mortality rates during the Crimean War by reconfiguring a pie chart, varying the length, rather than the width, of the wedges, so that the graph resembled a cock's comb. As the historian Hugh Small notes, Nightingale may not have invented statistical graphs, but "she may have been the first to use them for persuading people of the need for change".

THE RIGHT SLICE

Playfair's graphic innovations went beyond the pie chart: he also invented the bar graph. Academics conduct studies about which Playfair invention performs better. Excel and PowerPoint may abound with pie charts, but not everyone is a fan. The data-visualisation pioneer Edward Tufte wrote that "pie charts should never be used". Dan Boyarski, a professor at Carnegie Mellon University, encourages his students to expand their horizons. He also concedes, however, that in some cases, like illustrating a budget, the pie chart is fine.

A CRITIC OF THE PIE CHART

Like many of his contemporaries, the design consultant Stephen Few bemoans the ubiquity of pie charts. Here, he explains his perspective:

You wrote an essay called Save the Pies for Dessert. Why do you dislike pie charts so much?

Pie charts are very popular, but it's rare that a pie chart does the job better than a bar chart.

So, it's fundamentally flawed?

When looking at parts of a whole, the primary task is to rank them to see the relative performance of the parts. That can't be done easily when relying on angles formed by a slice.

How come?

Our eyes just don't do that task well.

So why do people keep using them?

I think there's a basic appeal to the shape of a circle - a gut-level visual appeal.