Flow and transfer

Draws a quantity moving from source to destination with width as amount, so the losses along the way become visible.

Your paycheck lands on the first. By the 20th you are checking the balance and doing the arithmetic that never comes out right. You know the big numbers. Rent, the car, groceries. What you cannot say is where the rest went, and the 180 rows in your banking app will not tell you, because a list has no shape.

Flow and transfer draws a quantity moving from where it enters to where it ends up, and makes the amount visible as the width of the path it travels. Wide path, a lot moved. Thin path, little moved. A path that starts wide and arrives narrow is a loss, and the loss is usually the point. The family exists because arrows are cheap and quantities are not. Anyone can draw a box with an arrow leaving it. Only this form makes you say how much left.

It has five common renderers. A Sankey splits one source into destinations and carries the amount in the ribbon width. An alluvial does the same across several time steps, so you watch the mix re-sort and see which stream is taking over. A funnel is the case where every stage is a subset of the one above it, so the shape only narrows. A flow map puts the nodes where the things actually are and weights the arrows between them. A conversion pipeline is a funnel with the drop named at every gap, which turns the question from how much arrives into where it leaves.

Reach for it when something accumulates or goes missing and nobody can name the transfer that did it. It is weak at any single precise value. You can see that savings is the thinnest ribbon on the page, but you should read the number off a table, not off the drawing. And it goes quietly wrong if you let unlike quantities share one width. Hours and dollars in the same Sankey is two drawings pretending to be one.