The wikipedia definition is:
Sankey diagrams are a specific type of flow diagram, in which the width of the arrows is shown proportionally to the flow quantity.
Sankey diagrams are typically used to visualize energy or material or cost transfers between processes. They can also visualize the energy accounts, material flow accounts on a regional or national level, and also the breakdown of cost of item or services.
BizNalysis shared the video below, but it is overwhelmingly taken up by the custom SQL used for data preparation. Having said that, the groundwork of a Sankey is at that stage of the process, and it’s reassuring to see that the Tableau end of the process is pretty straight-forward:
Continuus Technologies posted this video in January 2017:
A video released by SuperDataScience in May 2017 adds to the guides relating to this chart type:
As is often the case with Tableau, this is a chart type which exploded onto the scene and sparked a series of posts from members of the community.
Personally, I like Chris Love‘s article as it’s thorough and guides you through what is quite a laborious preparation process. The article is on The Information Lab blog here:
Olivier Catherin provided an equally detailed guide:
Jeffrey Shaffer wrote a three step guide, commencing here:
and running into stages two and three. Jeffrey has even written and shared an Excel VBA Macro to ease the burden of data preparation for Sankey’s. Jeffrey is prolific when writing about Sankey’s, and wrote a re-viz post where he made his energy usage data far sexier than that he received from his energy supplier:
Sankey’s do look good, no question about that. They were over-used when they received their initial burst of publicity, but there are countless great examples.
Ben Moss created a genre-stretching small-multiple Sankey:
Chris Love accompanied his blog with a couple of examples, including this more complex Sankey:
I could add many more examples (just search for “Sankey” in Tableau Public!)