Better Chart of the Day
by Jon Peltier
Thursday, December 17th, 2009
Peltier Technical Services, Inc., Copyright © 2010.
Licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.
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?
Related Posts:
- Growth Rates in a Panel Chart
- Macs vs. PCs
- Line-XY Combination Charts
- Add Individual Target Lines To Each Cluster in a Column Chart
- Pareto Charts
- Peltier Goes Bar Hopping
- Clustered-Stacked Column Charts with Vertical Separators
- Antibiotic Effectiveness – A Study of Chart Types
- Seasonal Adjustment – Preliminary Approaches
- Simple Waterfall Chart with Up-Down Bars
Posted: Thursday, December 17th, 2009 under Chart Busters.
Comments: 15
Comments
Comment from David Gerbino
Time: Thursday, December 17, 2009, 9:45 pm
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
Comment from Tony
Time: Thursday, December 17, 2009, 10:58 pm
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.
Comment from Jon Peltier
Time: Thursday, December 17, 2009, 11:12 pm
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.
Comment from Naomi B. Robbins
Time: Friday, December 18, 2009, 9:48 am
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.
Comment from Jon Peltier
Time: Friday, December 18, 2009, 1:05 pm
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.
Comment from Gary
Time: Friday, December 18, 2009, 1:25 pm
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.
Comment from Jon Peltier
Time: Friday, December 18, 2009, 2:14 pm
Here’s one for Naomi, without the redundant labels:
Comment from Jon Peltier
Time: Friday, December 18, 2009, 2:16 pm
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:
Comment from Tony Rose
Time: Friday, December 18, 2009, 2:21 pm
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…
Comment from Jon Peltier
Time: Friday, December 18, 2009, 2:26 pm
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.
Comment from Naomi B. Robbins
Time: Friday, December 18, 2009, 4:53 pm
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?
Comment from Jon Peltier
Time: Friday, December 18, 2009, 6:16 pm
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)”.
Comment from Morten Eghøj
Time: Saturday, December 19, 2009, 3:35 pm
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 :)
Comment from Ray R.
Time: Thursday, December 31, 2009, 3:11 pm
Great redo of a highly flawed chart in my opinion.
Trackback from uberVU – social comments
Time: Tuesday, January 5, 2010, 10:49 am
Social comments and analytics for this post…
This post was mentioned on Twitter by Jon_Peltier: New on the PTS Blog: http://zz.gd/eb86c7 Better Chart of the Day…
Write a comment
I welcome comments from my readers. If you have an opinion on this post, if you have a question or if there is anything to add, I want to hear from you. Whether you agree or disagree, please join the discussion.
If you want to include an image in your comment, post it on your own site or on one of the many free image sharing sites, and include a link in your comment. I'll download your image and insert the necessary html to display the image inline.
Read the PTS Blog Comment Policy.