Radial Bar Charts

Written by Jeff Heard on December 15th, 2009

The other day, I was presented with a problem of visualizing a small 3-D Excel spreadsheet in a way that allowed the viewer to:

  • Compare columns for balance.
  • Compare the third dimension alternates (professors vs. grad students).
  • Compare the rows for balance.
  • Compare the overall sums.

What I came up with was this:

fte-diagram

Along the ring are the names of the columns of data in the spreadsheet.  On each spoke are the rows in the two layers of the spreadsheet visualized as bar charts.  Stretching counterclockwise are the bars for senior faculty.  Stretching clockwise are the bars for graduate research assistants.  In the center, visualized as bubbles of varying radii are the totals from both bar charts along the spoke.  Note the light, thin rings connecting each bar. These are designed to draw a viewer’s eye around the chart, connecting bar to bar visually to inform the viewer that comparison is relevant.

This technique is appropriate for smaller charts.  I have a feeling that too many columns would get to be too visually busy, although I suspect the chart’s behaviour as rows increase may well be more robust, especially if the bar chart was changed to an area chart.

3 Comments so far ↓

  1. Anonymous says:

    Yeah I’m really conflicted about this one. I like the radial thing but my problem is that the radial aspect is not area preserving, also it means that lines of equal height are not of equal value and vice versa. So a radial histogram would be all wrong.

    It is a real balance I guess, if you just had straight spokes it might not look as good either and like you said, might not direct you around the chart.

  2. Nicolas says:

    I agree with anonymous, but at the same time I think that the visualization is still useful for comparing bars standing on the same concentric circle.

    Say for example that you’re using this visualization for the programming language benchmark. You chose one language (say, haskell -lol), and a set of languages to compare to (OCaml, Clean, Python, Ruby).

    On each barchart you’d be comparing Haskell to another language, each bar would stand for a particular programming test (binary trees, etc). Then it would be clear what language implementation was faster in a particular program, and for how much. Comparing bars in different concentric circles doesn’t make any sense in this example either, so no problem with the area preserving thing.

    Also, the bubbles in the middle could give you a good idea of the overall test comparison for both languages.

    I really like the viz :)

  3. Oliver Mooney says:

    To solve the area-preserving issue of the radial bars, you could instead use an n-sided polygon, with one side for each category (giving a hexagon in this case). There would be an upper limit to n, of course. Unless the radial presentation was chosen for more than just aesthetic reasons?

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