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?
David Gerbino says
Jon,
great job showing a better way to show the data. I was able to find at a glance where Apple passed Microsoft on the line chart version.
I still find it amazing how many people still show time series data as bar charts.
Thanks.
@dmgerbino
Jon Peltier says
Thanks for the comments, David and Tony.
I like to keep the markers in place to show exactly where the data points are. In this case they help to show the nonuniform spacing of the data.
Tony says
I’m with David on this one. Time on the x-axis almost always should trigger the thought of lines.
This is a great find Jon. The month spacing is perplexing and makes me question how the heck they decided on those months, which is less obvious in their version of the chart.
Here’s a tip for the readers – If you have to tilt your head 45-90 degrees to read a chart, it’s probably not designed correctly. ~ there’s your sign ~
I am a big fan of your version, though I might remove the markers.
Naomi B. Robbins says
What an improvement! Great job. But do you really need all those Ms on the vertical
axis when it is labeled “millions of users”? I’ve seen graphs labels thousands with tick marks 1000, 2000, 3000, etc. In some cases they mean 1000 thousands or a million and in other cases the labeling was redundant.
Jon Peltier says
Naomi –
Caught me again. In fact, I noticed the redundancy with the Ms and the “Millions of Users” after I’d hit the publish button, and decided I’d write about excessive labeling in a future blog post.
Gary says
Also interesting would be the growth rates and absolute # changes for the 6-month period… RIM looks like about 40% total growth; Apple 80+%, MS close to zero, hard to say on the little ones. On a numbers basis RIM appears to be keeping pace w/ Apple, which is interesting too.
Jon Peltier says
Here’s one for Naomi, without the redundant labels:
Jon Peltier says
Gary –
To compare growth rates, we can convert the Y axis to a logarithmic scale:
That one spreads out the axis scale too far, since Excel 2003 only uses powers of ten for the min and max of a log scale. But I know afew tricks, so here’s one with a nice log scale:
Jon Peltier says
Tony –
Yeah, I was thinking about that too. But I thought a light gray wasn’t too disruptive.
Another problem is that the irregularly-spaced log scale gridlines I added in the last chart fall in front of the lines and markers, because I hacked it and used error bars.
Coming soon: a technique to simulate gridlines that puts the lines behind (most) other chart features.
Tony Rose says
Another little option to clean up the chart since we are nit picking with the M’s is to remove the outline that you have in gray. By doing that, the labels will be easier to read too. Just because Naomi started…
Naomi B. Robbins says
Most intelligent readers would recognize a equally spaced scale of 0.1, 1, 10, 100 as a log scale. Does the next one, which certainly improves the spacing of the data, need some explanation?
Jon Peltier says
Naomi –
Who’s making the charts here, anyway?
Joking aside, as usual, you’re right. The axis label should saysomething like ” Millions of Users (log scale)”.
Morten Eghøj says
http://www.engadget.com/2009/12/18/iphone-nabs-46-pecent-of-japanese-smartphone-market-the-tiny-ja/
One more mobile graphs which could need some cleaning :)
Ray R. says
Great redo of a highly flawed chart in my opinion.