A Sankey diagram is an interesting visualization that uses the thickness of arrows to depict the flow-volumes in a system. The thicker the arrow, the more flow of energy, mass, or volume. Sankey graphics are easily read and quickly comprehended.
In this article, we’ll explore the creation of Sankey diagrams using Visio, and we’ll offer our own free Visio Sankey diagramming shapes for your downloading and diagramming pleasure!
What do Sankey Diagrams Look Like?
You can see many samples of Sankey diagrams by image-searching for “Sankey Diagram” on Google or MSN. You’ll see hundreds of colorful examples that will make you want to start diagramming right away! MSN’s Live Search offered these at the top of the result list:
If you work in any kind of industry in which material- or energy flow is important, or are working on environmental issues, then you’ll surely want to pull a Sankey diagram out of your hat at that next departmental meeting!
Can Visio do Sankey?
While there are no Sankey Diagrams templates that ship with Visio, there are a few in-the-box shapes that can be used to create rudimentary Sankeys.
Visio’s Block Diagram Template and Blocks stencil have shapes that you can use to create Sankey diagrams. Here we can see the Block and Arrow shapes at work in an oversimplified visual of an oil-combustion process:
A nice feature of the arrow, is that you can right-click the shape, and choose to have an open- or closed tail. This makes the outputs look better, as they blend nicely with the process box.
The alignment box (green handles) however, doesn’t match the body of the shape. And since the arrow-thickness is of primary importance in a Sankey diagram, it would make sense to have the body of the arrow exactly match the height of the shape. The arrow head “flanges” are superfluous, and could be outside of the box, so to speak.
Another problem comes when the arrow is lined up with the edge of the process box. When the tail is open, there is a little tab that sticks out and covers up the edge of the process box. The Visio-supplied arrow doesn’t quite get it right, as we can see when we zoom in:
Visio Guy Does Sankey
We’ve made a new version of the arrow shape which is more suitable to making Sankey diagrams. You can download it at the end of this article and give it a whirl!
There are improvements to the existing shape’s features, plus a few additions to make your Sankey-ing more pleasurable…
First, the alignment box matches the thickness of the arrow, so you can more directly control the “size of the flow”. It also makes it easier to position the arrow relative to the process box or other flow arrows.:
You’ll also notice the curios icons floating below the shape. These are Smart Tag menus that allow quick access to the shape’s features. You can also right-click the shape and gain access to all the features, but the Smart Tag menus are shorter and clearer, since they are divided into three groups for: Tail behavior, formatting, and arrowhead behavior.
When you right-click the arrow shape, you’ll see a dizzying array of features, which we’ll visually illustrate here:
The features allow you quick access to the Fill Format dialog, three styles of arrowhead, three lengths of arrowhead, and the choice to open or close the tail of the arrow.
The Color… menu item makes it easier and quicker to change the fill colors, so you can create interesting effects like this:
You can see that setting the Arrowhead Style to Point makes it easier to stack the arrows next to each other for a more compact diagram. It’s also easier to see that the ratio (by mass) of carbon-dioxide is roughly three times that of water in the combustion process. (I forgot to show air as an input, by the way…)
Arrowhead Aspect Ratios
One note about the arrowhead styles. When the style is Arrow, the arrowheads resize proportional to the body size. This ensures that the arrowheads maintain the same aspect ratio, and keeps the diagram’s appearance clean:
When the arrowhead style is Point, however, the arrowhead length stays constant. This looks better when the arrows are stacked together:
It’s a fine point, if you’ll pardon the pun, but it’s one that you don’t notice until its done wrong!
Sankey Diagram Resources
Sankey Diagrams on Wikepedia. Always a good place to start for definitions and links to other resources.
Sankey-Diagrams.com A person named Phineas runs this site and claims that A Sankey diagram says more than 1000 pie charts. Phineas loves Sankey diagrams and has created a whole blog about them. He breaks down the various types of Sankeys and analyzes diagrams that appear in the wild. Very interesting and informative.
e!Sankey A $100 software product which is dedicated to creating Sankey diagrams. You can download a trial version and give it a test drive! e!Sankey is the younger brother of the more fully-functional Umberto, which is a complete management system for modelling, calculating, and visualizing energy flow systems.
Sankey Helper is a free tool that creates Sankey diagrams in Microsoft Excel. This makes a lot of sense, since the flow-data for your system likely lives in a spreadsheet already!
Sankey Editor is another offering, from developers in Arnold Schwarzenegger’s lovely home town of Graz, Austria.
Sankey Diagram Software list I just found this great list of Sankey-related software from our Phineas over at sankey-diagrams.com.