Datawrapper’s policy on bad graphs
Datawrapper is a tool that lets you turn a dataset into a decent-looking chart within minutes. In an interview, co-founder Mirko Lorenz said Datawrapper is designed to prevent people making misleading graphs:
With Datawrapper, we try to make it as hard as possible to take data and create misleading charts with it. For example, it’s not possible to create bar charts with cropped axes. From time to time, users ask us to add this feature, but we never have and we never will. (via)
This may sound a bit paternalistic but it makes sense: Datawrapper’s philosophy is to offer a simple, robust way to quickly create a chart. If you don’t like the limitations, learn to code D3.js.
But Lorenz’ remark made me curious: would there be more design options, besides bar charts with cropped axes, that Datawrapper deems unacceptable? And are they limited to chart designs that are outright misleading, or do they more generally ban designs that result in ineffective or inaccurate data communication? Here’s an exploration of Datawrapper’s bad graph policy.
Y-axis not starting at zero
Datawrapper disapproves of y-axes that don’t start at zero in bar and column charts, but it allows them in line charts. I think this is consistent with the consensus on the topic.
I’m using the term spaghetti chart in the non-technical sense, meaning a chart with many lines that create an indecipherable mess. Datawrapper doesn’t ban spaghetti charts.
Long the chart type we all loved to hate, the pie chart has recently been sort of rehabilitated. I think many people would now agree that pie charts are a legitimate way to represent proportions. That said, 3D and exploding pie charts are still suspect. Datawrapper allows pie (and donut) charts, but doesn’t seem to allow 3D or exploding pie charts.
Using perspective to create a 3D effect will make it difficult to compare the sizes of elements in a chart. Fortunately Datawrapper doesn’t seem to allow any type of 3D chart.
Stacked bar chart
The rehabilitation of the pie chart coincided with a renewed critique of stacked bar charts: «basic bar charts are clearly better than pie charts, but stack them and they’re worse!». Which, by the way, doesn’t mean that it’s always wrong to use stacked bar charts. Datawrapper allows them.
Some charts have have a secondary y-axis, so different scales can be used in one chart (here’s an awkward example, source). There may be situations where this is defensible, but in general it shouldn’t be considered good practice. Datawrapper doesn’t seem to allow this.
Pictograms instead of bars
Some designers try to jazz up bar charts using pictograms instead of bars, forgetting to take into account that if you double the height of the pictogram, its area increases fourfold. The distortion is even worse when the pictograms are drawn to appear three-dimensional. Datawrapper doesn’t seem to allow replacing bars with pictograms.
The most well-known example of y-axes not starting at zero are cropped or truncated axes which start at a value higher than zero, but there are also examples of axes starting at a negative value. Edward Tufte points this out in The Visual Display of Quantitative Information, using a chart from an annual report as an illustration: «A careful look at the middle panel reveals a negative income in 1970, which is diguised by having the bars begin at the bottom at approximately minus $4.200.000». ↩
You can make a spaghetti chart interactive, for example let users click a label and the corresponding line will be highlighted. But this may still be an awkward solution, especially on mobile. ↩
«They can be useful when the point is to show that a value is the sum of other values, but you’re only interested in comparing the totals. They also work if you only need to show one section and can make that the one on the bottom. Then the bars are comparable and work well. But just throwing values into a stacked bar chart is a bad idea», Robert Kosara argued. Here’s how Dutch minister Jeroen Dijsselbloem messed up. ↩