I often read the Chart of the Day feature on the Silicon Alley Insider. It’s kind of a pop look at something relevant to the technology industry. The charts are a bit more cerebral and way less chart junkie than those in USA Today, and I like to just have a peek to make sure they stay honest.
A few months back they had a bar charts with a value axis that started above zero, and we can’t have that, now, can we? But I must say, these daily charts do not often violate good practices, and while they are somewhat decorated, it is usually limited to eye-catching series coloring and not splashy chart trash.
In iPhone Blows Past Windows Mobile the chart of the day showed the growth in users of half a dozen smart phones during 2009. From the title of the post, I expected to see lines crossing at some point. but they didn’t go for that effect. I’ve recreated their chart below.
The chart has several problems. First, the time scale moves vertically instead of horizontally. Second, the time points are not evenly spaced. The gaps between measurements alternate between three months and two months. Third, there is no immediate view of anything crossing anything else. The user has to work to extract that information.
A fourth problem is that the ends of the bars seem to trace a smooth curve from Google in February through RIM in October. Well, except for Microsoft, and you could even infer that the chart shows Microsoft as better than the rest. This is a spurious relationship resulting from the accidental alignment of the points grouped this way.
I put on my Chart Busters cap and went to work. The result is the chart below.
I’ve changed the time scale to horizontal, left to right. I placed the data points at proportional positions along the axis. I’ve changed the aspect ratio of the chart. And I used a line chart rather than a bar chart. What is now clear is the obvious growth of the iPhone past the stagnant Windows Mobile. And that was the point of the Chart of the Day article, wasn’t it?