# Alluvial plot vs. Sankey diagram

Is there any difference between an Alluvial plot and a Sankey diagram? Are these two names for the same thing?

## 1 Answer

I'm not sure there's any consensus on this.

Wikipedia says that an alluvial diagram is a type of Sankey diagram "that uses the same kind of representation to depict how items re-group"

RAWGraphs likewise says:

Alluvial diagrams are a specific kind of Sankey diagrams: they use the same logic to show how the same set of items regroups according to different dimensions.

Azavea says:

A Sankey diagram visualizes the proportional flow between variables (or nodes) within a network. The term “alluvial diagram” is generally used interchangeably. However, some argue that an alluvial diagram visualizes the changes in the network over time as opposed to across different variables.

Datasmith says they "are profoundly different types of diagram":

Alluvial plot:

• Shows how a population of facts is allocated across categorical dimensions.
• Left/right position has no particular significance; dimensions could be in any order.
• ‘Nodes’ are lined up in columns.
• Is useful for showing how features of a population are related — for example, answering questions like ‘how many people have features A and B, compared to how many have B but not A?’

Sankey diagram:

• Shows how quantities flow from one state to another.
• Left/right position shows movement or change.
• ‘Nodes’ could be anywhere, and must be laid out by an algorithm.
• Is useful for showing flows or processes where the amount, size, or population of something needs to be tracked — for example, answering questions like ‘out of the energy in system A, how much came from systems B and C and where will most of it go?’

This seems opposite of the Azavea definition?

The Data Visualisation Catalogue Blog tries to distinguish between them:

Like with a Flow Chart, a Sankey Diagram can include cycles, which is something that distinguishes them from Parallel Sets and Alluvial Diagrams.

Also, the flow paths in a Sankey Diagram can combine or split apart at any stage of the system’s process. Whereas on Parallel Sets and Alluvial Diagrams, you tend to get a group of flow paths only going from one side to the other.

Parallel Sets and Alluvial Diagrams aren’t too different from one another. However, the main difference between these two chart types is that Parallel Sets display a part-to-the-whole relationship, while Alluvial Diagrams only visualise quantities between dimensions.

Parallel Sets will have line-sets that are all uniform in length, while Alluvial Diagrams will have a lot more variation.