Bar chart races 101: Abbott Katz explains

By Abbott Katz 

The masses love them, the cognoscenti aren’t sure, but either way, they’re heading to a URL near you. The object of this melange of affection and ambivalence? Bar chart races, the data viz that’s sprinting across axes all over the internet.

Bar chart races – we’ll call them BCRs, the better to trim the word count – depart from their venerable static-bar-chart first-cousins by setting their bars in motion, in order to plot their data against a movable timeline. Consider by way of illustration the pioneering BCR authored by the Financial Times’ John Burn-Murdoch (the link will deliver you to the actual, in-motion chart):

Bar charts circa 1521

Here the chart adduces the world’s eight most populous cities circa 1521, the year referenced in the chart’s lower-right quadrant. By 1845, the chart looks like this:

The screenshots and the actual chart are worth studying (one doesn’t view a BCR so much as one plays it), because they exhibit the multiple streams of motion loosed by the BCRs:
1. The years flit by as they’re counted off.
2. The population values fronting the bars likewise change, of course.
3. The bars representing the cities relentlessly dispossess each other as the chart churns ahead, ranking and re-ranking themselves manically in a high-velocity game of demographic musical chairs.
a. And that means, among other things, that the chart jiggles its bars along both the horizontal (population change) and vertical dimensions (the city rankings) at the same time.
4. The value, or X-axis, raised here to the rafters of the chart, changes as well.

Note in addition that it’s perfectly possible for a bar to shrink en route if its current value falls beneath the preceding one. Bar chart races, then, are competitions in which the entrants sometimes run backward – and sometimes even disappear.

All of which raises a question: do the video-game-like displays orchestrated by BCRs smack of gimmickry or some gossamer form of “entertainment”, as software developer Mike Bostock opines in Stephen Gossett’s review article of the BCR phenomenon? Very possibly they do; but one person’s gimmickry is another person’s visual enhancement, after all.

A simple bar or column stuffed with a graphic, or even one festooned with a fetching colour, might qualify as a gimmick, too, albeit of the low-tech sort. Of course, BCRs would hardly be the first vizzes to be charged with gimmickry. 3D pie charts, for example, have had the boffins reaching for their firearms for some time now.

But another grievance brought against the BCR, a more substantive one, is their very hyperactivity. According to some critics, the charts freight viewers with a profusion of information – even as they deliver too little of it. To these naysayers, the bars’ riotous bursts across the chart run roughshod over and past the data, leaving little time for viewers to reflect on what they’re seeing; but at the same time, the doubters add that BCRs reduce their message to a series of one-point-at-a-time flashes of illumination.

That latter judgment calls for a bit of expounding. It alleges that as the bars streak past their chronological signposts they can divulge but a single instance of time – e.g. 1521 or 1845 – at any instant. In this regard, the Gossett piece cites Tableau’s Andy Cotgreave’s view that a garden-variety, workaday line chart might be more equal to the task – because it spreads out a series of time-points synchronically, enabling the viewer to see them all in one perusal.

That’s true, but the BCR might yet be the tool of choice at least for certain data scenarios. Consider, for example, the Burn-Murdoch chart. Because it spans 319 years’ worth of data, a line chart would have to unroll either a vast or a forbiddingly crowded, X-axis comprising those 319 points – and that’s literally a bit much.

And because, for example, New York City simply wasn’t there in 1500, its data series won’t even make its appearance in a line chart until 1624 or so. On the other hand, Vijayanagar, the world’s second-most populous city in 1521, is gone. Thus a good many of the lines in the line chart would be broken and/or partial ones. It’s beginning to sound messy.

Or consider a BCR rendition of say, a 100-meter dash – a bar chart race capturing an actual race, as it were. If for example runner times could be gleaned for each 1-meter interval, a BCR could vividly recapitulate the race, depicting the frenetic changes in runner positions and calibrating the respective finishes (the fact that the “fastest” bar – that of the winner – will have achieved the smallest number (i.e. the fastest time), can be dealt with; Its bar needn’t be the shortest). Don’t expect this kind of drama from a line chart.

But at the same time, the Burn-Murdoch chart instates a key static ingredient amid all the movement teeming elsewhere in the chart: the bar length of the most populous city – the one always holding the uppermost position in the chart – remains immutably fixed. Thus, the bar signifying Beijing’s world-topping 679,000 population in 1521 (the first screenshot) maps identically to the one accounting for London’s 2,103,000 residents in 1845, (in the second shot).

And don’t dismiss that curious constancy as a fluke of Burn-Murdoch’s BCR. Quite the contrary – a locked-in highest-value bar looms as a near-universal feature of the BCR genre. All the charts I dialed up on YouTube, for example, revealed a determinedly inert first bar, a likely function of the code authored by providers such as Flourish and Observable (Mike Bostock’s firm), whose platforms underpin so many BCRs.

Perhaps they should call that first bar the treadmill – it races, but isn’t going anywhere.

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