A Swiss software company features a screenshot on their website, depicting a thermal energy model for a building. I’m not mentioning the source, because it is a bit embarassing…

Despite the general good impression of the diagram and the tech labelling of the arrows, the width of these arrows seems completely arbitrary. Well, to be fair … they don’t call it a Sankey diagram.

After being AFK for a while, here’s a quiz for you: What’s wrong in this Sankey diagram?

Something is wrong here ….

Not only does the arrow ‘light energy’ branch out behind the other arrow without causing a reduction in magnitude for the remainder ‘heat energy’. But also 1000 J is split into two arrows of 90 J and 10 J.

And while still in ‘mild rant’ mode, here is another one from an educational website…

I have nothing against large companies providing free didactic materials like videos and images to support education. But the below Sankey diagram samples from the image bank of a large multinational company are a fail!

Teachers should better not use them in class, as their smarter students may identify the fundamental error in them:

Can you spot the error?

Phineas got hold of a design study through one of his informants… Looks as if at least one of the large manufacturers of tablets is working on a dedicated ‘Sankey Diagram Tablet’. It is expected that either Apple’s next iPad, the new Samsung Galaxy Tab, or possibly Microsoft’s tablet with Surface surface will be Sankey diagram enabled. Further details in regard to the technical specifications are unknown…

Well, I am waiting anxiously for this new product release, and have prepared my sleeping bag to camp out the night at the doors of the retail shop to be the first to get hold of it.

Happy april fools day! 😉

As some of you might know, I also like to post a diagram from time to time that has, … mmmh, say …. has the potential of being improved. This one, found on the website of a German consulting firm, is such an example.

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I am glad they don’t call this a Sankey diagram anywhere. Everything that could go wrong did go wrong here. The horizontal arrow segments all have the same width, probably due to the fact that the diagram was prepared by combining rectangles. The added outflows that leave vertically at the bottom are much wider than the horizontal first segment. And the outflows are not to scale when being compared among each other (check the 5% arrow commpared to the neighnouring 11% arrow that should have roughly the douuble width. OMG!

A presentation from 2005 on the French energy flows included the Sankey diagram below (I prefer not to name the author or the link to the original source, in order not to embarass anybody).


This Sankey diagram is pretty much messed up, and definitely a candidate for the “Worst Sankey Diagram Contest” that has already been called for. It took me a few seconds to understand that the flows dangling vertically below the blue arrow are actually a breakdown of the 177 mtep consommation finale. Vraiment … j’ai vu mieux que ça!

This is more or less how I would do it. Less colors, a breakdown of the blue flow into the five consumption sectors.

Below is a great example of how to misguide the viewer’s interpretation of data in a Sankey diagram. Found this one on presentation slides somewhere on the web.

The two arrows branching off to the top in a 90° angle do not maintain their magnitudes, which supposedly represent the quantities, and are drawn at a deliberate width. On top of that, the bases of the arrowheads are about two times as wide as the actual arrow width, thus overemphasizing the flow. Look at the 40% thermal losses which look much larger than the 50% useful work to the right side…

I did play around a little bit with this tiny example, and came up with a number of alternative versions.







Not sure which one is the “best” one, and each has its pros and cons. #1 (hover the mouse pointer over the image to see the number of each alternative version) is very close to the original version. The arrow head size in #3 is more modest. #4 has no explicit spike arrow heads at all. #6 has grey divider lines on most of the horizontal section. I kind of like #7 with color differentiation best, but then again, it is energy that is displayed in all flows.

What do you think? Let me know your favourite or suggestions for improvements in your comment