Kelp Diagram
Colored bands that weave through a sequence of elements, showing how set memberships evolve over time — like seaweed strands connecting members of each group.
// 01 — The chart
What it looks like
A Kelp diagram showing how committee memberships change across four legislative sessions. Colored bands connect members of each committee.
// 02 — Definition
What is a Kelp diagram?
A Kelp diagram (also called a KelpFusion diagram) visualizes set membership that changes over time or across a sequential ordering. Named for its visual resemblance to kelp strands weaving through water, it uses colored bands or ribbons that thread through a series of elements positioned along a timeline.
Each colored band represents a set (or group). The band passes through every element that belongs to that set at each time point, curving smoothly between them. When an element joins a set, the band extends to include it; when an element leaves, the band bypasses it. This creates an organic, flowing visualization that shows the temporal dynamics of group membership.
Unlike static set visualizations (Venn, Euler, UpSet), Kelp diagrams add the dimension of time or sequence. They answer questions like: “Which members joined this committee in the third session?” or “When did these two groups stop sharing members?”
Origin: Introduced by Wouter Meulemans, Nathalie Henry Riche, Bettina Speckmann, Alec Jacobson, and Daniel Weiskopf in their 2013 paper on visualizing sets over time, building on earlier Euler-diagram-based approaches for dynamic data.
// 03 — Anatomy
Parts of a Kelp diagram
// 04 — Usage
When to use it — and when not to
- Set memberships change over time and you need to show that evolution
- Tracking which elements join, leave, or switch between groups across sessions
- Visualizing committee memberships, team compositions, or cohort movements
- Showing how clusters or categories shift in a spatiotemporal context
- You need an alternative to animation for conveying temporal set dynamics
- Set memberships are static — use Venn, Euler, or UpSet plots instead
- You have too many sets (>6–8) — bands become tangled and unreadable
- You have too many elements (>30–40) — the diagram becomes overcrowded
- Precise quantitative comparisons are needed — bar charts are better
- Your audience is unfamiliar with the format — it's a niche visualization
// 05 — Reading guide
How to read a Kelp diagram
Follow these steps to interpret a Kelp diagram.
Identify the sets by color
Each colored band represents one set or group. Check the legend to understand which color maps to which group.
Follow a single band across time
Trace one band from left to right. The dots it passes through are the elements belonging to that set at each time point.
Note where bands expand or contract
When a band picks up new dots, the set has gained members. When it bypasses dots it previously included, members have left.
Look for shared elements
Elements (dots) touched by multiple bands belong to multiple sets at that time point. Overlapping bands at a dot indicate shared membership.
Identify structural changes
Bands that merge, split, appear, or disappear indicate major group dynamics — mergers, schisms, formation, or dissolution of groups.
// 06 — Pitfalls
Common mistakes
Too many overlapping bands
When bands cross and overlap extensively, the diagram becomes a tangled mess. Limit the number of sets or use alternative visual encodings (color intensity, separate panels) for complex data.
Poor element placement
The layout algorithm for positioning elements significantly affects readability. Poorly placed elements create unnecessarily long or crossing bands. Use optimization-based layout algorithms.
Missing legend or color key
Without a clear color legend, readers cannot identify which band represents which set. Always include a visible legend, especially with more than 3 sets.
Ignoring band width as a variable
Some implementations use band width to encode set size. If band widths vary, explain what they represent — otherwise, keep them uniform to avoid misinterpretation.
// 07 — In the wild
Real-world examples
Legislative committee tracking
Political scientists use Kelp diagrams to visualize how legislators move between committees across legislative sessions, revealing patterns of influence and specialization.
Sports team roster evolution
Analysts track how player rosters change across seasons, showing trades, retirements, and draft picks as elements joining and leaving team-colored bands.
Research collaboration networks
Bibliometricians visualize how research groups evolve over time, showing which scientists collaborate in which periods and how teams form, grow, and dissolve.
// 08 — Quick reference
Key facts
// 09 — Variations
Variations of the Kelp diagram
KelpFusion
Combines Kelp bands with Euler-style hull regions at each time step, showing both the threading connections and the spatial grouping of elements.
Bubble Sets + time
Uses isocontour hulls around set members at each time step, with implicit connections between time steps rather than explicit bands.
LineSets
A simpler variant using thin colored lines instead of wide bands, reducing visual weight but sacrificing some readability at the cost of cleaner layouts.
// 10 — FAQs
Frequently asked questions
What is a kelp diagram?+
A Kelp diagram (also called a KelpFusion diagram) visualizes set membership that changes over time or across a sequential ordering. Named for its visual resemblance to kelp strands weaving through water, it uses colored bands or ribbons that thread through a series of elements positioned along a timeline.
When should you use a kelp diagram?+
Use a kelp diagram when set memberships change over time and you need to show that evolution. It also works well when tracking which elements join, leave, or switch between groups across sessions, and when visualizing committee memberships, team compositions, or cohort movements.
When should you avoid a kelp diagram?+
Avoid a kelp diagram when set memberships are static — use Venn, Euler, or UpSet plots instead. It is also a poor fit when you have too many sets (>6–8) — bands become tangled and unreadable, or when you have too many elements (>30–40) — the diagram becomes overcrowded.
What is another name for a kelp diagram?+
Kelp Diagram is also known as KelpFusion, temporal set diagram. The name varies between fields, but the visualisation technique is the same.
Is a kelp diagram suitable for dashboards?+
Yes — a kelp 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 kelp diagram?+
Kelp Diagram belongs to the Sets 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.