You are NOT spider man, so why do you use radar charts?

Posted on September 18th, 2008 in Charts and Graphs , ideas , Learn Excel - 19 comments

you-are-not-spiderman-face-maskThere are few charts in excel that are as revolting as a radar chart. The purpose of a radar chart is to compare m options across n parameters so that audience can be convinced that option A is better than say option B. But, I am yet to come across a radar chart that tells out this story screaming loud.

Despite all this I see many consultants using Radar Charts mainly because they do some complex analysis on decision options and need to show a complicated chart to prove the point in board rooms.

But they still suck, arent they? I mean human eye is not trained to go around circles 4 times stopping at 6 different parameters only to realize that all the options are equally bad (good).

Take a look at this radar chart and tell me if you can interpret anything

ulgy-excel-radar-chart-consultants-enemy

Ok, Radar Charts are unreadable, what is your idea?

Even though we can not process 24 data points by a glance, we can do a better job at understanding the options and indulging in a discussion or better still concluding something when same data is presented differently. Here is where I guess Petal Charts can help.

Excuse the name, but Petal charts are nothing but tweaked radar charts that segregate the information yet somehow provide comparability. Take a look:

Download petal chart template in excel and play with it.

How to create this petal chart?

  • Take the usual radar chart data and re-tabulate it:
    See the example below:
    radar-chart-excel-data-tablepetal-chart-radar-alternative-data-format

    Why should you do it? Because petal chart is nothing but a tweaked radar chart. So a 4 by 6 radar chart converts to 4 by 24 petal chart.

  • Now select the new tabular data and create a regular radar chart with area. This will create the petal chart.
  • Finally tweak the colors and axes.
  • That is all. You now have an interesting way to tell your story. What do you think?

Here is another example of a sample petal chart.

petal-chart-radar-alternative-excel

Remember: download the petal chart template excel workbook and play around.

Spiderman Photo from Flickr.

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19 Responses to “You are NOT spider man, so why do you use radar charts?”

  1. Jon Peltier says:

    You cheated by putting the first petal chart next to the radar chart. They are plotting different data. The petal data on a radar chart would be a set of concentric hexagons, and it would gbe easier to make comparisons than the petal chart.

    The last petal chart, the one with ragged petals, corresponds to the radar chart. And I think it shows how ineffective a petal chart is. The reader has to visualize what part of the second petal corresponds to the low part of the first petal, and it’s rotated around by 90°. However bad the radar chart is, the petal chart is worse. Prettier, but worse.

    Hate to be boring, but the best alternative is some kind of line chart. I’ll write a short blog entry in the morning. I’ve already done the charts, and they aren’t too ugly.

  2. John Gardner says:

    I monitor a circular array of 27 temperature sensors on the outlet of a natural gas fired turbine, and when I suspect a temperature imbalance I use a radar plot, which can be oriented to correspond exactly to the real-world physical locations of those sensors. The axis is temperature, and this gives a very good visualization of hot or cold zones. This is the only application I have seen where the radar plot is intuitive.

  3. Chandoo says:

    @Jon… Agree with you. The two images were reversed. I have corrected the post. Didnt mean to cheat or anything. I wrote and scheduled this post a while back and didnt realize the mistake. Thanks a ton for pointing it out.

    Also, I agree to your point that a line chart is a perfect alternative to radars, My attempt is not to propose these petal charts as *the* alternative, but just as another fun charting option.

    Waiting for your post :)

    @John… Welcome to PHD Blog :)

    You have a really good point. In your case the radar actually became a map because of the orientation / location of the turbines. It makes perfect sense to use the radar to see temperature trends.

    But, often, for most data the radar orientation has little meaning for the plotted values and that is where petal charts can be one alternative.

  4. Jon Peltier says:

    John -

    Good example. Of course it works because you’re using the radar chart as a map, as Chandoo points out. A similar usage is a wind rose.

  5. Is this becoming the gallery of bad charts? The radar plot and especially the petal plot create the wrong impression of the data, because they essentially convert lengths into areas. Your posting here made me finally finish my discussion of that problem, see Linear vs. Quadratic Change

  6. Jon Peltier says:

    Robert -

    Chandoo has a knack for picking controversial topics. Good post about areal data encoding.

    • Rod says:

      I use a radar (spider) chart to plot progress in comparing yearly audits. I color 1 series solid and reflect the series for the new year as a line over top. By reversing the polar axis you can see when there’s improvements or loses. However, this usage is optical and does not rely on the user interpolating data. i.e. smaller concentric area = better

  7. Chandoo says:

    @Robert… I agree with you that radar / petal plots convert lengths to area without meaning it. Your post on Linear vs. Quadratic is quite insightful.

    @Jon… Agree, What is a blog with out discussion?

  8. I’m all for discussion, I just don’t understand PHD’s motivation. Criticizing a chart and then providing an Excel file is like saying “It’s bad to poison your neighbor’s cat, but here’s a list of good poisons and places to get them.” I don’t need to poison my neighbor’s cat to figure out that I shouldn’t do it, and I don’t need to see my own data in a radar chart to know it’s a bad idea.

  9. Chandoo says:

    @Robert … I agree that radar charts are not a very good way to show various decision alternatives (atleast that is what these charts are mostly used for)

    That is where the petal charts come in to picture, they take familiar radar and turn it in to something where you can see all alternatives and how they have performed on a set of attributes.

    All I said in the article is ..

    “Here is where I guess Petal Charts can help.

    Excuse the name, but Petal charts are nothing but tweaked radar charts that segregate the information yet somehow provide comparability…. You now have an interesting way to tell your story. What do you think?”

    I am sorry if the article sounded like “replace all radar charts with petals” but the intention at PHD is always to show alternatives. And they are good and bad things about them.

    I am happy to learn that petals / radars unintentionally convert lengths to areas.

  10. Jon Peltier says:

    Robert -

    I’m not sure if you’re critiquing Chandoo’s approach or Excel’s. Chandoo is making a suggestion, saying, here’s something, try it out. Well, I tried it, decided it’s not an improvement over the radar chart, and I’ll write a short post explaining why, and suggesting that people stick the the tried and true line chart variations.

    Ford had the Edsel, Chandoo has the petal chart, and for a long time my web site had a speedometer-type chart for Excel. It was wildly popular, and I could have gotten rich charging people to implement it. But I finally realized it went against the other lessons I was trying to get across. So it’s gone.

    Excel has lots of ways to skin a cat. Some are quite painful, in terms of 3D types and pies and the like, and others are quite ugly, with nasty colors and effects (including the awful defaults). Some are ugly and painful. Sometimes I think my role is to work with the masses who use Excel daily, and help them find attractive and painless ways to get their tasks done.

  11. derek says:

    Chandoo, where is the data that made your original unreadable radar chart? The download file just contains some tame tidy data that isn’t the same.

  12. Chandoo says:

    @Jon… thanks for that. I use this blog to learn a ton of stuff, blurting out the techniques as I use / find them out so that many more perspectives can be gathered. It makes me happy when tons of people like what I say here. But it makes me wiser when passionate people like you make sure that I understand the mistakes of things I say here. And that is precisely why I write, to become better.

    @Derek … the excel is just a template, I am not sure if it had the data used in the post. Feel free to change it as you wish and I am sure it should produce the unreadable chart you have seen in this post.

  13. [...] you use petal charts at all? In petal charts – an alternative to radar charts, I have proposed a radar chart hack that can used replace radar charts. I know that it is not a [...]

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  16. Brian says:

    In my experience, radar charts, if properly used, are intuitive and revealing to a large number of people. In your example it is immediately obvious that whatever is represented by the orange polygon is a high-performance, high-functionality, hard-to-use item- like specialist software. The entity represented by the blue line is a low-performing, easy-to-use item, like simple software with a nice gui, but not very extensive capabilities. The other two are in-between and their specific differences can be observed and compared. What is so hard about that? If those are the messages you want to get across, the radar chart does it reasonably well, and in my opinion, better than the petal charts.

  17. [...] similar effect can be seen in the petal chart or star glyph, which connects points on a number of axes that radiate from a common point. Whether [...]

  18. Shrey says:

    Hi Chandoo,

    My firm uses radar charts to show EFQM audit results for the entire company.

    Outer circle is 100% and all points are like SCM, Quality Assurance, Maintenance etc. with two series one showing the previous audit results and a thick one showing this audit results.

    This approach I find clearly shows improvements(or deterioration) in each aspect quite clearly. I agree the same data might be shown effectively using colum or bar graphs, but at least here I find the use of RADAR Chart to be quite effective.

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