The most under-used chart in business

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In 1898, Irish engineer Captain Henry Sankey published a flow diagram to show how much energy a steam engine was wasting between coal and motion. The chart did one thing exceptionally well. It made waste visible at a glance.

The Sankey exposes where value flows, splits, concentrates, or disappears.

More than a century later, the chart still does that job better than any alternative, yet it remains the most under-used chart in business communication.

A bar tells the reader how big something is. A Sankey tells them what the size is made of.

For teams explaining divestitures, capital allocation, customer journeys, or talent flows, that difference is the entire decision.

Each context below corresponds to a question executives already ask in board rooms and quarterly reviews.

Market structure. A market overview written as a 12-page slide deck buries the structural answer in narrative. A Sankey delivers it in one frame.

The LATAM telecom view shows four operators absorbing the region's revenue and the geographies each one depends on, exposing concentration, geographic dependence, and competitive overlap in a single read.

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M&A and divestitures. The Telefónica LATAM exit Sankey resolves a multi-country divestiture in one frame.

Total 2024 revenue of €41.3 billion splits into divested operations (Argentina, Chile, Peru, Colombia, Mexico) and retained core markets (Spain, Brazil, Germany), with each divested business labeled by acquirer (Telecom, Millicom, Integra Capital, OXIO).

Investors see the buyer, the asset, the scale, and the remaining footprint in a single read.

The chart's range extends well beyond corporate finance. Here are four more cases worth the treatment.

Customer journeys. A funnel collapses every path into a single tube, hiding where users actually branch, stall, or leak. A Sankey shows the channel that brought them in, the product they landed on, the segments they moved through, and the moment they churned. The chart exposes which acquisition channels feed retention and which feed waste, a distinction most cohort views never reveal.

Talent flows. HR dashboards report headcount by function and attrition by quarter, but they rarely show the connections between them. A Sankey traces hires into roles, internal moves between functions, and exits by destination. Patterns the dashboard buries become visible at a glance: which functions act as feeder pools, which roles serve as exit ramps, and which competitors absorb the talent the company trained.

Capital allocation. Budget tables list dollars by segment and project, but they answer the wrong question. The board wants to know what each dollar produced. A Sankey reframes the same data as flow: capital enters at the top, splits into segments, distributes across projects, and lands in outcomes. The story the board wanted (where the money went and what it returned) emerges from the chart structure itself.

Energy and emissions. ESG reporting demands a clear path from emission source to category to scope, and most decks reduce this to a stacked bar that loses the chain of causation. A Sankey preserves it. Scope 1, 2, and 3 emissions trace from operational source through transformation to end disclosure, which is why regulators, auditors, and rating agencies still treat the Sankey as the gold standard for emissions reporting.

One additional example sharpens the market structure case. The following Sankey traces 9,919 active satellites by orbital class into operator share. The left column splits into LEO, GEO, and Elliptical/MEO.

The right column ranks operators by total. SpaceX alone accounts for 6,370. The chart converts a market-share question into a structural one: whose satellites occupy which orbits, and how concentrated the LEO layer has become.

A bar chart of operator counts hides the orbital dependency. The Sankey makes it the headline.

1. The Source / Target / Value structure

Every Sankey reduces to a table with three columns. Build the table first. The chart follows.

Using the Telefónica example:

That table renders the chart shown above. Add a second tier (Argentina → Telecom; Chile → Millicom; Mexico → OXIO) and the same logic extends. Most Sankey failures begin when the analyst opens the tool first and asks it to invent the structure. The structure exists in the data. Build it on a spreadsheet, paste it in, then style.

Before any Sankey leaves your hands, run it against five questions. Each one corresponds to a failure mode that turns a clean chart into a wall of ribbons.

→ More than 15 flows on screen? Group everything below 2% of total into "Other." The reader does not need every name. They need to know who matters.

→ Is color carrying information, or just labeling? Color is a second axis. Use it to mark the headline (SpaceX, divested vs. retained, source vs. target). When every node has its own color, color tells the reader nothing.

→ Are labels readable from across the room? If the smallest label requires the reader to lean in, the chart has answered the wrong question. Cut the small flows or absorb them into "Other."

→ Does one flow draw the eye first? A good Sankey has a hierarchy. The reader's eye should land on the headline before it explores the rest. If everything is the same weight, nothing is.

→ Can you state the chart's argument in one sentence? If not, the chart is decorative. Either cut it or split it into two simpler charts that each carry one argument.

The rule. Every Sankey should answer one question. If it answers two, it answers neither.

Four sentences carry the chart.

The script forces discipline. If line 3 cannot be stated in one sentence, the chart is not ready. If line 4 cannot be stated, the chart is decorative.

Tooling note. Flourish handles the structural rendering. Canva polishes typography and final layout. Bertrand Seguin's work at App Economy Insights sets the upper bound: company P&Ls rendered as instantly readable flow systems.

The Sankey rewards the analyst who knows the answer before drawing the chart. It is not a discovery tool. It is a communication tool, and a strict one. Used well, it compresses a deck into a frame.

If these tools changed how you think about presenting flow data, they will likely sharpen someone else's view too.

Forward this issue to your team or to one colleague who builds decks for boards, owns a P&L, or has ever stared at a Sankey wondering where to start.

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