Where Sankey diagrams came from: Minard, Sankey and modern earnings charts
The Sankey diagram is one of the few chart types named after a person who did not invent it, and one of the few that has been independently rediscovered by three separate fields.
Minard and the march on Moscow
Charles Joseph Minard's 1869 map of Napoleon's Russian campaign is the famous ancestor: a band whose thickness is the size of the surviving army, thinning as it crosses the continent. It encodes six variables at once and needs no legend, which is why it still appears in every data visualisation course.
Sankey and the steam engine
In 1898 the Irish engineer Matthew Henry Phineas Riall Sankey published a diagram of energy flow through a steam engine, showing how much of the input became useful work and how much became loss. Engineering adopted it, and the name stuck to the format.
The finance rediscovery
The recent wave came from investor communities publishing quarterly earnings as flow diagrams: revenue entering, costs branching off, profit surviving. It spread because it compresses a filing into one image that survives being screenshotted, which is how financial information actually travels now.
Why it keeps coming back
Every field eventually needs to show a quantity being divided and losing something at each step. That problem has one good visual answer, so the format gets rediscovered rather than replaced.
Draw a modern one in a minute →The tooling has changed completely and the grammar has not: sources on the left, stages across, width equals quantity, and losses drawn honestly.
Frequently asked
Who invented the Sankey diagram?
The technique predates the name. Charles Minard used it in 1869; Matthew Henry Phineas Riall Sankey published his engine efficiency diagram in 1898, and the format took his name.
Why are Sankey diagrams popular in finance now?
Because an income statement is a flow, and one image that shows how much revenue survives as profit travels much further on social platforms than a table of figures.