Sankey Diagrams

Found this Sankey-like diagram accompanying an abstract submitted for the 2001 International Conference on Thermal Engineering and Thermogrammetry. Posting it here on the blog before this site eventually vanishes. This Sankey diagram is a good example of how not to draw Sankey diagrams, I think. Or, as a Japanese friend would put it politely: “Maybe… [turn head at 30° degree angle, make slight air-sucking noise by inhaling through open mouth] … maybe not so good”.

Here’s the diagram:

The idea was to display heat losses at a slab furnace in a Turkish steel plant. Heat losses were identified in exhaust gases (22 %), at the cooling pipes (2.90 %), and at the furnace walls (0.47 %).

The fact that the widths of the arrows displaying the heat losses were chosen arbitrarily give a completely wrong idea of the proportions. The powerpointish curved arrows don’t really contribute to a better understanding.

All in all, not a very good one. Adding this to my “Lying with Sankey diagrams” mini series (see part 1, part 2), which has been neglected recently.

This diagram of sun radiation being absorbed and reflected when hitting earth (from Solar Energy Facts website) is a rather weak remake of the original Nasa diagram.

I find the floating powerpointish arrows kind of disturbing, and with the arrow magnitudes not to scale, would even call it misleading. Took the time to prepare two new versions of it (actually I am beta testing the new version 2.0 of e!Sankey at the moment - so this was a nice little test case).

The first version sticks more to the original idea of the diagram shown above, but the arrow magnitudes are corrected and to scale. The second version is closer to the original ‘Breakdown of the incoming Solar Energy’ diagram by User A1 that can be found on Wikicommons. The latter one has the flow for energy being absorbed by atmosphere (33 PW) branching off as the first arrow horizontally.

The below Sankey diagram of the ‘Material Flows of Japan in the FY 2000′ has been published by the Japanese Ministry of Environment (環境大臣) and has been reproduced in a number of publications and presentations (sample PPT). Similar charts, representing the inputs into the Japanese economy and the outputs are available for subsequent years.

When I copied the values of the Sankey diagram and re-designed it (see pic 1 below), it quickly became obvious that the inputs (2130 Mio. tons) don’t match the Outputs (2386 Mio. tons). After some research I finally detected the reason for the mismatch in a footnote to the diagram in a press release by the ministry. It said that, “due to intake of moisture, etc., total output shall be larger than total material input.” This footnote might have been dropped unintentionally when using the diagram in other publications. I wouldn’t really call this “lying” (as the title of the post implies), but maybe negligence. I wonder if anyboy doubted the numbers when looking at the diagram?

In the second diagram below I adjusted this difference of 256 Mio. tons on the input side.

Another rather surprising thing in this Sankey diagram is the fact that the domestic food consumption within Japan (127 Mio. tons/year in 2000) was almost as high as the total quantity of material being exported (132 Mio. tons). Taking into account, for example, the number of cars being exported from Japan, and their weight, this sounds a little unlikely. However, I think that many of the produced goods might be hidden in the “Net Addition to Stock”.

And for the readers who study Japanese … Sankey diagram : サンキーダイアグラム

I have decided to present in a loose sequence some diagrams I have found on the web that are obviously wrong. Or -let’s put it in other words- don’t reflect the numbers appropriately. Well, we all know that this happens quite often, and if you plan to do that purposely this book might be of use for you…

So, here is the first sample from an Estonian energy portal page:

I kind of like this Sankey diagram, because it is simple, colorful, and even though I don’t speak Eesti, I more or less get the meaning of it.

However, have a look at the gray flow labeled “Muu auru tarbimine” which supposedly represents 2% of the overall energy. Shouldn’t it be much thinner, compared to the other flows? I think this ‘not-to-scale’ representation is owed to the fact that in a diagram set up with a conventional drawing tool (is it Power Point they used?) would be very hard to draw and the label couldn’t be placed inside. So they decided to make it “small” but at the same time “lying” with this diagram.

It is also quite funky how the purple arrow for “Kaod” has an arrow line pretty much to scale, but the arrow head is much fatter!
Ah well, and the percentage values don’t add up to 100% and the percentage values for the green flows (”Pasöörid” and “Pihustuskuivatamine” - I love that word!) are percentiles of the yellow “Aur” flow in contrast to the other percent indications.

Here is the same Sankey diagram but with the values to scale, automatically created with a Sankey diagram software. I have adjusted the percentiles in accordance with the absolute values given.

Do you have an interesting Sankey diagram to share? Send it to phineas@sankey-diagrams.com