Circos Plot
A circular visualization originally from genomics showing relationships between segments arranged on a ring — ribbons or links inside the circle reveal interactions, rearrangements, and flows between different regions.
// 01 — The chart
What it looks like
A Circos plot showing genomic translocations between six chromosomes. The outer ring represents chromosome segments, while interior ribbons reveal structural rearrangements between distant regions.
// 02 — Definition
What is a Circos plot?
A Circos plot is a circular visualization that arranges data segments around a ring and uses ribbons, links, or arcs inside the circle to show relationships between them. Originally developed for comparative genomics, it has become one of the most recognizable visualizations in biology and is now used across many domains.
The outer ring is divided into ideograms — segments that represent entities such as chromosomes, countries, or departments. Each segment’s arc length is proportional to its size. Inside the circle, ribbons connect positions on one segment to positions on another, showing translocations, trade flows, migrations, or any pairwise relationship.
What makes Circos uniquely powerful is its ability to layer multiple concentric data tracks between the ring and the center: heatmaps, histograms, scatter plots, and line plots can all be stacked to provide a rich, multi-dimensional view of the same entities. This layering capability is why it became the standard for genome-wide visualizations.
Origin: Circos was created by Martin Krzywinski at the BC Cancer Agency’s Genome Sciences Centre in 2009. It was designed specifically to visualize genomic rearrangements in cancer genomes, where translocations between chromosomes needed to be shown in a compact, publication-ready format.
// 03 — Anatomy
Parts of a Circos plot
// 04 — Usage
When to use it — and when not to
- Showing translocations, fusions, or rearrangements between chromosomes or genomic regions
- Visualizing migration, trade, or flow data between a moderate number of entities (5–30)
- You want to layer multiple quantitative tracks (heatmaps, histograms) around the same ring
- The circular layout helps emphasize the cyclic or symmetric nature of the data
- Creating publication-ready figures for genomics or bioinformatics research
- Comparing structural variations across multiple samples on the same coordinate system
- You have only a handful of relationships — a simpler chord diagram or even a table would suffice
- Your audience is unfamiliar with circular layouts and precision matters more than aesthetics
- You need exact value comparisons — curved ribbons make precise quantitative judgment difficult
- The number of segments exceeds 40–50, making the ring too crowded to label meaningfully
- A linear layout (e.g., a Sankey diagram) would communicate the same flows more intuitively
- Interactive exploration is not available and the static image has too many overlapping ribbons
// 05 — Reading guide
How to read a Circos plot
Follow these steps to interpret a Circos plot, whether in genomics or any other domain.
Read the outer ring segments first
Each colored arc on the outer ring represents an entity — a chromosome, a country, a department. Its length is proportional to size. Identify what each segment represents using the labels.
Follow the ribbons across the circle
Each ribbon connects two positions: where it starts and where it lands. The width of the ribbon at each end may differ, indicating the magnitude of the flow in each direction. Thicker ribbons mean stronger relationships.
Check the inner data tracks
Many Circos plots layer additional data between the ring and the center — heatmaps showing expression levels, histograms showing density, or scatter plots showing individual data points. Read these tracks from outside (ring) inward (center).
Look for crossing patterns
Ribbons that cross the center of the circle connect distant segments. In genomics, these often represent translocations or structural variations. The more crossing ribbons, the more rearranged or interconnected the data.
Compare ribbon density between segments
Some segments may have many ribbons while others have few. This asymmetry reveals which entities are most connected or most involved in the relationships being visualized.
// 06 — Common mistakes
Mistakes to watch out for
Too many ribbons creating visual spaghetti
When hundreds of ribbons overlap in the interior, the plot becomes unreadable. Filter relationships by significance or magnitude, use transparency, or consider showing only the top N connections. Interactive highlighting on hover can also help.
Inconsistent segment ordering
Segments should follow a meaningful order — chromosome number, geographic position, or alphabetical. Random ordering forces the reader to search for segments, and ribbons will cross unnecessarily, adding visual noise.
Neglecting color differentiation
When all ribbons are the same color, it becomes impossible to trace which segment they originate from. Color-code ribbons by their source segment or use a gradient to show directionality.
Overloading with too many data tracks
Circos supports many concentric data tracks, but stacking more than 3–4 layers makes the plot dense and hard to parse. Show only the most relevant tracks and consider splitting into separate panels for different analyses.
Using Circos when a linear layout is clearer
The circular layout is visually striking but can obscure simple patterns that a Sankey diagram, chord diagram, or even a matrix would show more clearly. Choose Circos when the circular arrangement adds genuine insight, not just aesthetics.
// 07 — Real-world examples
Where you’ll see Circos plots used
Genomics: Cancer genome structural variants
Circos was originally designed for this use case. Researchers visualize whole-genome sequencing data showing translocations, inversions, and copy number changes across all chromosomes simultaneously. The outer ring shows ideograms, with concentric tracks for copy number, expression, and mutation data, while interior ribbons mark structural rearrangements.
GenomicsGlobal trade: International merchandise flows
Economists use Circos-style plots to show trade volumes between countries or regions. Each segment represents a nation, with arc length proportional to total trade volume. Ribbons show bilateral trade flows, with width indicating magnitude. This reveals dominant trade corridors and trade imbalances at a glance.
EconomicsEcology: Species interaction networks
Ecologists map pollination networks, predator-prey relationships, and symbiotic interactions using Circos. Segments represent species or functional groups, and ribbons show the strength of interactions. The circular layout naturally accommodates the many-to-many nature of ecological webs.
Ecology// 08 — At a glance
Quick reference
// 09 — Variations
Types of Circos plots
The Circos framework supports several visual configurations depending on the data being shown.
Link-only Circos
Shows only ribbons/links between segments without additional data tracks. Clean and focused on relationships.
Multi-track Circos
Stacks multiple concentric data tracks (heatmaps, histograms, scatter) for rich multi-dimensional views.
Half-Circos
Uses only a semicircle, saving vertical space. Often used for comparing two conditions side by side.
Stacked Circos with highlights
Combines data tracks with selective link highlighting to focus attention on specific relationships of interest.
// 10 — FAQs
Frequently asked questions
What is a circos plot?+
A Circos plot is a circular visualization that arranges data segments around a ring and uses ribbons, links, or arcs inside the circle to show relationships between them. Originally developed for comparative genomics, it has become one of the most recognizable visualizations in biology and is now used across many domains.
When should you use a circos plot?+
Use a circos plot when showing translocations, fusions, or rearrangements between chromosomes or genomic regions. It also works well when visualizing migration, trade, or flow data between a moderate number of entities (5–30), and when you want to layer multiple quantitative tracks (heatmaps, histograms) around the same ring.
When should you avoid a circos plot?+
Avoid a circos plot when you have only a handful of relationships — a simpler chord diagram or even a table would suffice. It is also a poor fit when your audience is unfamiliar with circular layouts and precision matters more than aesthetics, or when you need exact value comparisons — curved ribbons make precise quantitative judgment difficult.
Is a circos plot suitable for dashboards?+
Yes — a circos plot 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 circos plot?+
Circos Plot 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 circos plot?+
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.