Notes

A type of flow diagram that shows proportionality, e.g. the arrows/items are sized.

They are often used when mapping out transfers of something, maybe energy or money. For example, could show the different parts of the system where energy is lost in transit before reaching it's destination or it could show where all the money goes if there are many "middle-men" involved in the transfer.

Basic info on wikipedia This website is dedicated to sankey diagrams