Bubble Treemap
A treemap variant that replaces rectangles with packed circles — each bubble’s area represents its value, and nesting reveals the hierarchy.
// 01 — The chart
What it looks like
Nested circles group divisions by business segment. The cloud division dominates, while smaller divisions like IoT and gaming are immediately visible by their bubble size.
// 02 — Definition
What is a bubble treemap?
A bubble treemap is a visualization that combines the hierarchical structure of a treemap with the circular layout of a bubble chart. Instead of subdividing a rectangle into smaller rectangles, it uses packed circles nested within parent circles to show how a whole is divided into parts at multiple levels.
Each circle’s area is proportional to its data value. Parent circles contain their children, making the hierarchy visible through containment rather than just adjacency. The result looks like a cluster of bubbles within bubbles.
Compared to rectangular treemaps, bubble treemaps sacrifice some space efficiency (circles don’t tile perfectly, leaving gaps) but gain in visual clarity: the nesting hierarchy is immediately obvious, and the uniform shape of circles makes area comparison easier than comparing thin rectangles with varying aspect ratios.
Key tradeoff: Bubble treemaps use about 10–15% more space than rectangular treemaps due to gaps between circles. This inefficiency is the cost of the clearer hierarchy and better aspect ratios.
// 03 — Anatomy
Parts of a bubble treemap
// 04 — Usage
When to use it — and when not to
- Hierarchy visibility matters more than space efficiency
- You want to clearly show grouping/nesting relationships
- The visual aesthetic of circles is preferred over rectangles
- Comparing area is important — circles have uniform aspect ratios
- Building engaging, presentation-quality visualizations
- Space efficiency is critical — gaps between circles waste 10–15% of available area
- You have many small leaf nodes — tiny circles become illegible quickly
- Precise area comparison is needed — while better than rectangles, circles still require estimation
- The hierarchy is flat (one level) — use a standard bubble chart instead
- You need to fit labels inside all circles — small bubbles can't hold text
// 05 — Reading guide
How to read a bubble treemap
Identify the hierarchy levels
The outermost circles are parents, containing smaller child circles. Nesting shows which items belong to which groups.
Compare circle sizes
Larger circles represent larger values. Circle area (not diameter) is proportional to the data — a circle twice the area represents twice the value.
Read the color encoding
Colors typically distinguish categories at a specific hierarchy level. Check the legend to understand what each color represents.
Look for dominant clusters
Which parent group contains the most volume? The largest parent circle with the most child bubbles is the dominant category.
Check labels for detail
Read the text inside or beside each bubble for the category name and value. Hover or click interactions may reveal more detail in interactive versions.
// 06 — Data format
What the data looks like
| Division | Segment | Revenue |
|---|---|---|
| Cloud | Platform | $42B |
| Cloud | AI/ML | $18B |
| Cloud | IoT | $8B |
| Software | Office | $28B |
| Software | CRM | $12B |
| Entertainment | Gaming | $15B |
| Entertainment | Streaming | $5B |
// 07 — Construction
How to build one
Calculate circle radii from data values (radius proportional to square root of value for area encoding).
Pack child circles within parent circles using a circle-packing algorithm.
Size parent circles to tightly contain all their children plus padding.
Pack parent circles within the outermost container.
Apply colors by category, add labels, and use opacity or stroke to distinguish hierarchy levels.
// 08 — Common mistakes
Mistakes to avoid
Encoding value by diameter instead of area
If circle radius is directly proportional to value (instead of area), larger values are dramatically exaggerated. Always use area encoding: radius ∝ √value.
Too many hierarchy levels
More than 3 nesting levels makes the chart visually overwhelming. Flatten the hierarchy or focus on a specific branch.
Ignoring the whitespace
Circles leave gaps when packed together. Don't try to make these gaps meaningful — they're an artifact of the geometry, not data.
Unlabeled small circles
When circles are too small for labels, provide tooltips or an interactive legend. Never leave circles completely unidentified.
// 09 — In the wild
Real-world examples
Government budget breakdowns
Showing how federal spending is allocated across departments, with sub-divisions visible as nested bubbles within each department's circle.
Technology ecosystem maps
Visualizing the landscape of tools and platforms within categories like databases, frameworks, and cloud services.
Organizational structure visualization
Representing team sizes within divisions — each team as a bubble nested within its department's circle.
// 10 — Quick reference
Key facts
Also known as
Circle treemap, nested bubble chart
Category
Part-to-whole
Best for
Hierarchical data with clear nesting
Ideal levels
2–3 hierarchy levels
Key advantage
Clear hierarchy + uniform aspect ratios
Tradeoff
10–15% less space-efficient than rectangular treemaps
// 11 — Accessibility
Making it accessible
Use distinct colors with sufficient contrast for each hierarchy level.
Add ARIA labels describing the hierarchy: 'Cloud segment containing 3 divisions: Platform ($42B), AI/ML ($18B), IoT ($8B)'.
Provide a data table alternative showing the full hierarchy with values.
Ensure all bubbles have either visible labels or accessible tooltips.
Use stroke colors or patterns in addition to fill color to distinguish groups for colorblind users.
// 12 — Variations
Chart variations
Flat Bubble Chart
A single level of packed circles without nesting — simpler, for non-hierarchical data.
Zoomable Bubble Treemap
Interactive version where clicking a parent bubble zooms in to show its children at full scale.
Force-directed Bubble Layout
Uses physics simulation to position bubbles, allowing them to spread out rather than pack tightly.
// 13 — FAQs
Frequently asked questions
What is a bubble treemap?+
A bubble treemap is a visualization that combines the hierarchical structure of a treemap with the circular layout of a bubble chart. Instead of subdividing a rectangle into smaller rectangles, it uses packed circles nested within parent circles to show how a whole is divided into parts at multiple levels.
When should you use a bubble treemap?+
Use a bubble treemap when hierarchy visibility matters more than space efficiency. It also works well when you want to clearly show grouping/nesting relationships, and when the visual aesthetic of circles is preferred over rectangles.
When should you avoid a bubble treemap?+
Avoid a bubble treemap when space efficiency is critical — gaps between circles waste 10–15% of available area. It is also a poor fit when you have many small leaf nodes — tiny circles become illegible quickly, or when precise area comparison is needed — while better than rectangles, circles still require estimation.
How is a bubble treemap different from a treemap?+
Both a bubble treemap and a treemap can look similar at first glance, but they answer different questions. Reach for a bubble treemap when the comparisons and patterns it was designed to reveal match what you need to communicate, and choose a treemap when its particular strengths better fit your data and audience.
What is another name for a bubble treemap?+
Bubble Treemap is also known as Circle treemap, nested bubble chart. The name varies between fields, but the visualisation technique is the same.
What size of dataset works best for a bubble treemap?+
Bubble Treemap works best for Hierarchical data with clear nesting. Outside that range the chart either looks empty or becomes too cluttered to read clearly.
Are bubble treemaps accessible to screen readers?+
Yes — a bubble treemap can be made accessible to screen readers by pairing it with a clear text summary of the key insight, ensuring color choices meet WCAG contrast guidelines, adding descriptive alt text or aria-label to the SVG, and offering the underlying data as an HTML table fallback for assistive technologies.