Sankey Diagram vs Chord Diagram: Which to Use
A chord diagram shows the volume between every pair of groups around a circle; a Sankey shows it from a start column to an end column. Compare them and choose the right one.
A chord diagram and a Sankey can show the same table of movements between groups. The chord arranges the groups in a circle, the Sankey puts the sources on the left and the destinations on the right.
The example is 1,000 people and where they lived at the start and the end of a year: North, South or East. The data is a three-by-three table, and the Sankey draws it with the start on the left.
The Sankey makes direction and the start-to-end comparison plain. The chord is more compact when there are many groups and the direction matters less.
The same table
Both charts draw a from-to table. A chord puts each group once on a circle and joins pairs with bands. A Sankey puts each group twice, as a source and as a destination.
Where they differ
Reading direction is the main difference, and the number of groups is the second.
- Sankey: direction is built in, start on the left.
- Chord: direction is shown by band ends and is easy to miss.
- Chord: stays compact with ten or more groups.
- Sankey: the staying-put flows are visible as straight ribbons.
Choosing
With a handful of groups and a clear before and after, use a Sankey. With many groups and a symmetric question about exchange, a chord can be the more compact picture.
Key points
- 650 of the 1,000 people (250 + 200 + 200) end the year where they started.
- North ends with 350 people, South with 360 and East with 290.
- The largest move is 100 people from North to South.
- The figures are invented.
The example’s data
Invented figures, balanced at every node.
| From | To | Amount (people) |
|---|---|---|
| North at start | North at end | 250 |
| North at start | South at end | 100 |
| North at start | East at end | 50 |
| South at start | North at end | 60 |
| South at start | South at end | 200 |
| South at start | East at end | 40 |
| East at start | North at end | 40 |
| East at start | South at end | 60 |
| East at start | East at end | 200 |
The same data as CSV
source,target,value
North at start,North at end,250
North at start,South at end,100
North at start,East at end,50
South at start,North at end,60
South at start,South at end,200
South at start,East at end,40
East at start,North at end,40
East at start,South at end,60
East at start,East at end,200How it works
Write the from-to table
Rows are the start group, columns the end group.
Give each group two nodes
One at the start, one at the end, with different names.
Enter each cell of the table as a flow
Include the cells on the diagonal.
Check the balance
Each start node should send on exactly the people it began with.
Frequently asked questions
Do chord diagrams do something Sankey cannot?
They stay compact with many groups, and they treat all groups equally with no left-to-right order.
What about a table with ten groups?
A Sankey of ten by ten is crowded. Group the smaller ones into Other or consider a chord or a matrix.
Edit this migration Sankey
Open the example as your own chart and enter your from-to table.
