Chord Diagram
A circular visualization that reveals relationships and flows between interconnected entities — the thicker the chord, the stronger the connection.
// 01 — The chart
What it looks like
A chord diagram showing trade flows between three major regions. Chord thickness represents trade volume.
// 02 — Definition
What is a chord diagram?
A chord diagram is a circular visualization used to display relationships and flows between entities arranged around a ring. Each entity is represented as an arc segment on the circle, and connections between entities are drawn as curved bands (chords) that span across the interior of the circle.
The width of each chord is proportional to the magnitude of the relationship it represents — a thicker chord means a stronger connection or a larger flow. This makes it possible to see both which entities are connected and how strong those connections are at a glance.
Chord diagrams excel at revealing mutual relationships in matrix data, such as migration between countries, trade between regions, or communication between departments. They are especially powerful when relationships are bidirectional and you need to see the balance of flows.
Origin: Chord diagrams gained popularity in the data visualization community through Mike Bostock’s D3.js library. The technique draws on circular graph layouts and adjacency matrix representations used in network science since the mid-20th century.
// 03 — Anatomy
Parts of a chord diagram
// 04 — Usage
When to use it — and when not to
- Showing flows or relationships between a set of entities (trade, migration, communication)
- Your data is a square matrix of mutual connections
- You have fewer than ~10–12 entities to keep the diagram readable
- Bidirectional flows are important and you want to see the balance
- You need a compact, visually striking summary of interconnections
- Audience is comfortable with moderately complex visualizations
- You have more than 12–15 entities — chords become impossible to distinguish
- Your audience is not familiar with circular layouts — use a simpler network chart
- You need to show hierarchical structure — use a tree or Sankey diagram
- Exact values matter more than relative comparisons — use a table or heatmap
- Connections are sparse — most chords will be invisible, wasting space
- You need to show directionality clearly — arc diagrams or Sankey diagrams are better
// 05 — Reading guide
How to read a chord diagram
Follow these steps whenever you encounter a chord diagram in the wild.
Identify the entities around the ring
Each colored arc segment on the outer ring represents one entity — a country, department, product, etc. Read the labels or legend to understand what each arc represents.
Compare arc lengths
The angular span (length) of each arc tells you the total magnitude of that entity's connections. Longer arcs mean more total flow in and out.
Trace individual chords
Each curved band connects two arcs. Follow a chord from one side to the other to identify which two entities are connected and by how much.
Read chord widths
The width of a chord at each end encodes the flow magnitude. If a chord is wider at one end than the other, the flow is asymmetric — more goes in one direction.
Look for dominant patterns
Step back and look for the thickest chords — these represent the strongest relationships. Also notice if some entities mostly send and others mostly receive flow.
// 06 — Common mistakes
Mistakes to watch out for
Too many entities on the ring
Once you exceed 12–15 arcs, chords become thin, overlapping, and unreadable. Aggregate smaller entities into an "Other" group or filter to the most significant connections.
Ignoring color consistency
Each entity's arc and its outgoing chords should share the same color. Inconsistent coloring breaks the visual logic and makes it impossible to trace connections from a specific entity.
No interactivity for dense diagrams
Without hover or click interactions to highlight individual chords, dense chord diagrams become visual noise. Always add interactivity when the number of connections is high.
Confusing directionality
Chord diagrams can encode directed flows (asymmetric chord widths), but readers often miss this subtlety. If direction matters, label it clearly or consider a Sankey diagram instead.
Using it for hierarchical data
Chord diagrams show peer-to-peer connections, not parent-child hierarchies. If your data is hierarchical, use a tree diagram, Sankey, or sunburst chart.
// 07 — Real-world examples
Where you’ll see chord diagrams used
Economics: Global trade flows between regions
A chord diagram showing import and export volumes between continents. Each arc represents a continent, and chords show bilateral trade. The asymmetric chord widths reveal trade imbalances — for example, one region exporting far more than it imports.
EconomicsGenomics: Gene co-expression networks
Researchers use chord diagrams to visualize which genes are co-expressed across chromosomes. Each arc is a chromosome segment, and chords connect co-expressed gene pairs, revealing clusters of genetic interaction.
BioinformaticsBusiness: Inter-department collaboration
A consulting firm maps email communication flows between departments. Thicker chords between engineering and product management reveal heavy collaboration, while thin chords to finance suggest siloed operations.
Organizational Analysis// 08 — At a glance
Quick reference
// 09 — Variations
Types of chord diagrams
The basic chord diagram has several important variants, each suited to different network characteristics.
Non-ribbon chord diagram
Replaces thick ribbon chords with thin lines, reducing visual clutter for dense networks where connection presence matters more than magnitude.
Arc diagram
Unrolls the circle into a line with arcs above, making it easier to read when entities have a natural linear order.
Directed chord diagram
Adds directionality with asymmetric chord widths or arrowheads, clearly showing which entity sends and which receives.
Grouped chord diagram
Groups related arcs together with gaps between groups, adding a hierarchical layer to the circular layout.
// 10 — FAQs
Frequently asked questions
What is a chord diagram?+
A chord diagram is a circular visualization used to display relationships and flows between entities arranged around a ring. Each entity is represented as an arc segment on the circle, and connections between entities are drawn as curved bands (chords) that span across the interior of the circle.
When should you use a chord diagram?+
Use a chord diagram when showing flows or relationships between a set of entities (trade, migration, communication). It also works well when your data is a square matrix of mutual connections, and when you have fewer than ~10–12 entities to keep the diagram readable.
When should you avoid a chord diagram?+
Avoid a chord diagram when you have more than 12–15 entities — chords become impossible to distinguish. It is also a poor fit when your audience is not familiar with circular layouts — use a simpler network chart, or when you need to show hierarchical structure — use a tree or Sankey diagram.
Is a chord diagram suitable for dashboards?+
Yes — a chord diagram can work well in dashboards as long as the panel is large enough for readers to perceive the encoded values, has a clear title, and includes the legend or axis labels needed to interpret it.
What category of chart is a chord diagram?+
Chord Diagram belongs to the Network family of charts. Charts in that family are designed to answer the same kind of question, so they often work as alternatives when one doesn't quite fit your data.
How do you read a chord diagram?+
Start with the axis labels and legend, then look at the overall shape before zooming into individual marks. Compare prominent features against the rest of the data, and verify any conclusion against the underlying numbers when precision matters.