The Viz Police: Picky, Picky but A Common Error
The Viz Police is a series of commentary on visual analysis in the wild, based on how well the chart in question conveys information. Charts that offend will be cited by the Viz Police.
A graphic in the LA Times recently offended the Viz Police in subtle but important ways: they left out two elements essential to nearly any graphic so it’s nearly impossible to walk away with a concrete understanding of the trend lines. Yes, we’re being picky (kind of like getting pulled over because your tags are out of date) but to understand the meaning of a data visualization you’ve got to know what the trend lines represent.
The vizualization is dramatic. Colors are distinctive and the lines are thick enough to get a decent idea of what’s going on. The title is descriptive, as is the caption.
And the copy below the graphic is useful and is as dramatic as the graphic.
For starters, I don’t know what that double-lined gray line and that nice thick black line are, nor do I know the time period the lines cover. For the sake of space, I suspect LA Times editors thought to drop the legend and axis to give room to the text. They probably expected people would click on the graphic to get to the bigger version, which does in fact have those elements. But there's nothing in this graphic that suggests I should click on it.
Since we’re being picky, let's talk about that block of text. Captions on graphics are normally a good thing - and this one is very well-written (expect nothing less from the LA Times). But reading on the web is really an act of scanning. So even the text below the graphic, while informative, is not shown in a way that encourages scanning. A few bullets would help.
Now on to the larger graphic itself. What’s amazing is that this is not just a bigger version of the same chart as what I saw previously: it actually extends the time period of the chart. And this extension makes the overall point far better than the smaller version. Below is what you see if you click on the image above.
The good news is that they've included the legend under the lines when they have not yet fallen so precipitously. But I wonder - since they have the space, why not put the legend underneath the graphic entirely leaving a big wad of white space to really dramatize the drop? I've synthesized it with some not-so-fancy cut & paste skills. I think having the legend off the chart communicates the drop better than having it on the chart.