Sankey Diagrams

I have been presenting “bad examples” of Sankey diagram before (like this one, or this one), and I have a few more in my collection.
The following one from an PowerPoint presentation by someone from PennState. The topic of the presentation is actually quite interesting: thermoacoustic refrigeration – using sound waves for cooling. It describes the results of a research project.

Unfortunately, this Sankey diagram has some shortfalls, which qualify it as being a “bad example”. These are:

• Sankey arrow widths are not always to scale (see for example the flow of 7.6 W in the middle labelled “surface”, which is definitely not half the width of the 14.6 W flow marked “Joule loss”)
• Arrows branching out of the main flow are shown as short stubs, just as if the quantity is represented by the length (!) of the arrow, rather than its width. A completely new concept for Sankey diagrams. Have a look at the 0.9 W mini-stub “Surface” in the cone area, and at the 1.2 W stub “Surface” in the linear motor box.
• The diagram uses dotted-dashed frames to mark sections in the diagram, at the same time it uses white arrows with a simple border line for the Sankey arrows. Either colored or grey areas, or colored Sankey arrows would have helped enormously.
• Arrows branch off orthogonally, and to accomadate for the reduced quantity in the remaining flow, the border of the arrow on the opposite side curves in. This is not wrong as such, but rather uncommon, and can best be observed in the linear motor section at the left. Same phenomenon for arrows joining the main arrow. The arrow heads just overlap rather than actually joining the other arrow graphically. The receiveing arrow bulges out on the other side.
• The section between the exhaust heat exchanger and the regenerator is awkward, and probably wrong. How can you branch off 296.6 W and 5.8 from a stream of 320.5 W, and are still able to have a flow of 63.0 W lead away from the remaining flow. I have not yet figured out what the problem is, but possibly the “Carnot minimum” flow was supposed to be drawn the other way round.

When I get to figure out the last issue I might draw this Sankey diagram myself, and post it here.

Does it take a hero like Daniel Ferry from the Excelhero blog to do a Sankey diagram in Excel? Well, you may not have to be a hero, but as Daniel puts it, this is “… seriously tedious work, as Excel has no native chart type to do what is required automatically.”

Daniel used the LLNL 2008 U.S. energy flow charts as model for his Sankey diagrams in Excel. Here is what he came up with (clipped section):

Actually the result is quite close to the original Sankey diagrams, with similar colours, arrow routing, and even the same fonts.

Daniel explains:

“I lightened the colors on the input boxes (had to do it), but otherwise I think my rendition is faithful to the original. I may have stayed too true to flow pipe proportionality. Some of them are so thin they do not print well. This should be addressed. While my pipes are seemingly lined up, they will not survive the chart being resized vertically without some small errors, either gaps in a pipe stack, or overlap.
(…)
An interesting project would be to create an Excel addin that would allow you to specify category box locations and have VBA do all of the grunt work in lining up the flow pipes, automatically creating the chart. (…) In it’s current form no VBA was used. “

So, if you wish to draw a Sankey diagram with the Microsoft Office package installed on your computer, and enjoy using VBA, you might want to give it a shot. Gabor Doka’s Sankey helper (an Excel macro) is another option. Dedicated Sankey diagram software tools are available. It would recommend one of those, if you need to produce more than one Sankey diagram, or wish to make updates to your diagram and layout adaptations more comfortably.

BTW, here is the story on the man behind the Sankey diagrams at LLNL.

I recently discovered Trefis and their Sankey-style diagrams as a visualization. Trefis models are used to determine the target stock price for companies, by looking at their product portfolios and playing around with the expected growth rates and market shares. Well, there is a whole model behind these interactive graphics, but the interesting part is that the share of the companies turnover is broken down by products, and is shown with proportional Sankey-like arrow magnitudes.

At the tip of the joint arrow head you can see the target share price, which is calculated as “the result of mathematically combining all of our forecasts for a company into a single number representing the per share value of the company.” When playing around with the parameters, this value will adapt accordingly.

Here are some examples

Forbes, techCrunch and the New York Times all reported about what the latter calls “America’s Next Top Stock Model”, but none of the mentioned Sankey diagrams though.

Have fun playing around with the models … they have fancy Web2.0-silverlightish animations too. But don’t blame me if the share doesn’t reach the forecasted price

Gabor Doka, developer fo SankeyHelper is currently working on SankeyTurtle, the implementation of a simple language for arrow routing in his Excel macro-based diagramming tool SankeyHelper. SankeyTurtle is currently being beta-tested.

The idea of SankeyTurtle code is to give each Sankey flux – each data cell – an accompagnying instruction how to draw the flux exactly in terms of path and geometry. The SankeyTurtle syntax is based on the vintage Logo TurtleGraphics drawing language, where you tell an imaginary turtle with a pen attached to it’s tail commands like “Move Forward” and “Turn Right 90°” and record the trail of the pen.

This will definitely an exciting improvement for all users of the SankeyHelper freeware … sorry, Sankeyware.

I’ll keep you posted about the progress and any official release.

Found the following Sankey diagrams in an educational presentation by UNIDO on Cleaner Production (CP).

This is actually quite a nice idea to show the improvements resulting from a technical measure. The diagram on the left represents the original situation, while on the right it is seen in grey. The flow diagram for the new situation overlays the “old” diagram. Both are scaled to 1 kg of varnish applied to a workpiece (the green Sankey arrow), so the reductions in input quantity and emissions show the actual savings achieved.

andycrellin posted an inquiry on the board of the Flowing Data, regarding software for drawing so-called source-destintation split diagrams. Nathany answered pointing to the Sankey software list on this blog. Thanks!

This is andy’s colorful sample. Quite nice. I especially like the color gradients along the bands, a feature which – to my knowledge – none of the software tools currently supports.

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

Following yesterday’s post with the translation of a blog post by Chiqui Esteban from infografistas.com here is the translation of the post “Caudales, erogación… ¿flujo?” of April 5, 2009. Again, I left some words in Spanish in square brackets.

– translation start –

Volume flow, distribution… flux?

A new chapter in the discussion [polémica] about the ‘scientific’ name of the “little arms” graphics ['gráficos de bracitos'].

Xocas came up with the name ‘volume flow’ diagrams ['gráficos de caudales'] and my vote was for ‘distribution diagram’. Other suggestions were thrown in: Xoán G. made reference to Minard and his ‘capacity diagram’ ['gráfico de aforo']. Herminio J. Fernández voted for cosmography diagrams ['cosmografías'] as refered to by Stovall [Infographics by James Glenn Stovall, Allyn&Bacon, Massachussetts, 1997]. Many others voted for ‘flow diagrams’ ['gráficos de flujo'], although Xocas discarded this suggestion because “the term flow diagram normally refers to a very specific type of visualization of process [flows]. It could be used as a generic term, but has interference with another model”.

Now, there is a new player in our conversation. It is Mario Tascón, who also believes that the correct denomination is ‘flow diagrams’. His justification:
“According to Harris (Information Graphics) and Bruce Robertson (How to make Charts and Diagrams) these graphics are called flow diagrams, and are of the type in the same category which are used as decision diagrams in informatics [computer science]. The latter are more in fashion now [Por motivos de modas], but the former have always [sic!] existed (a historic example is the one of Napoleons troops)”.

Suggestions are welcome in the comments.

– translation end –

I hope I got it more or less correct. It is not easy to find the right translation for the sometimes subtle differences between the terms. For those of you who can read Spanish, please check out the original post and the full discussion thread on Xocas’ blog.

The post is decorated with this beautiful Sankey diagram.

It shows the main earnings and spendings of Spain in 2008 and was produced by Jorge Doneiger and Álvaro Valiño for the daily newspaper Publico in 2007. Values are in million Euros. Flows are to scale, as for as I can see, the ‘impuestos especiales’ in dark black might be en exception.

The top part shows the sources of funding, the bottom part the beneficiary sectors. The fact that the stacked width in the middle is wider than that of the funds distributed suggests that the Spanish state is actually piling up its money, but probably this has to do either with the list of recipients not being complete, or with earnings received in 2008 but not distributed in the same year.

The hand with the coin supports Chiqui Esteban’s vote for naming it a ‘distribution diagram’. Toss a coin in the coffee dispenser and wait for your coffee to be poured… errh, did we have ‘dispenser diagram’ already?

I save the ‘best of comments’ and my reasoning why I still call them Sankey diagrams for another time…

Note (Aug 19): A case of DYRF, do your research first! I just detected that Chiqui himself has an English version of his article here. So, now you got the choice between two versions!