There is a tendency when producing dashboards to go for the cutesy-cutesy. Reader Daniel L. came across an attempt by Facebook to document its data center metrics (link). They chose this circular, spiraling design:

Notice that the lines of equal distance on a circular plot are the concentric circles. Thus, when they connect different points in a continuous way, as if it were a standard line chart, the line segments between data points are distorted. The diagram below shows the problem:

One potential advantage (although not worthwhile) of wrapping the data into a circle is that the 24 hours become a continuous line. Except that it isn't the case here! Weirdly, the purple and blue lines show a huge discontinuity at the ray that points vertically upwards from the origin. This leads to an even more fascinating find.

The circle actually rotates! It's like a rotating restaurant. The time shown vertically pointing upwards keeps changing as I write this post. This makes the discontinuity even more baffling. You'd think the previous data point just shifts anti-clockwise but apparently not. If any of you can figure this out, please leave a comment.

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As Daniel pointed out, the traditional line charts shown in the bottom half of the page would have done the job with less fuss. Not as eye-catching, but not as baffling either.

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One innovation of on-line charts is the replacement of axis labels with mouse-over effects. Mousing over the chart here produces the underlying data values. This is elegance.

One horrible trend with on-line charts is the horrendous choice of scale. Look at the top two charts, especially the orange line chart about power usage. It makes no sense to choose a scale that completely annihilates the underlying fluctuations.

I have found the same problems with many Google charts. It looks as if nothing is happening except when you look more closely, you learn that a tiny distance represents a big percentage shift in the underlying data.

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