Is a sunburst a pie chart?

It extends a part-to-whole radial display across multiple hierarchy levels.

What does an outer ring mean?

Greater depth in the hierarchy, not necessarily greater value.

Can categories overlap?

The underlying data can, but a part-to-whole chart needs an explicit counting or allocation rule to avoid misleading totals.

AI Glossary / Data science and analytics / Advanced

Sunburst chart

Definition

A sunburst chart displays hierarchical data as sectors arranged in concentric rings. The center represents the root or overall collection, and successive rings represent deeper levels of the hierarchy. Sector angles commonly encode a quantity such as a count or amount. It shows categories, subcategories and their contributions.

What it means

Read the chart from the center outward to follow a path through the hierarchy. A resource collection might divide first by topic and then by format. An outer sector belongs to the parent sector directly inward from it, so its position communicates membership as well as its numerical contribution.
The rings represent hierarchy depth, not automatically time, importance or a larger quantity. A sector farther from the center can have more visible area simply because it occupies a larger radius. Use the stated value, angle and labels rather than treating every sector's area across different rings as directly comparable.
A sunburst is most useful when the hierarchy itself matters. If the only question is which category has the largest count, a simple ordered bar chart may communicate the answer more directly.

How it works

Prepare a hierarchy with a label, parent relationship and value for each relevant node, or provide complete paths from the root to leaves. Repeated labels need distinct identifiers when they refer to different nodes. For example, “Video” under Business is not the same node as “Video” under Daily life.
Define the aggregation rule before plotting. A parent value may represent the total for its whole branch, or it may represent an additional amount beyond its children. Plotly exposes these alternatives through its total and remainder branch-value modes. Supplying branch totals as additional amounts can double-count the intended measure.
The chart allocates angular space to branches and their children. Color may identify categories or encode another variable, which requires an explanation. Interactive labels can show values and percentages, but the chart should specify whether a percentage refers to the parent or the entire collection.

Three practical examples

An editorial team shows resource counts by topic and format. Readers can follow each topic outward to see its mix of articles, videos and audio resources.
A service team groups requests by service area and request type. The display helps locate large branches for investigation, with a table available for precise comparisons.
A project team groups recorded hours by workstream and activity. It checks that each hour is allocated once before showing the hierarchy as parts of a total.

Think of it this way

A sunburst resembles a circular contents page whose branches widen according to a chosen measure. Moving outward reveals more detail within a section. The layout tells you where an item belongs, while the encoded quantity tells you how much it contributes. Interpret position and color using the stated rules.

Worked example

Suppose a fictional collection contains 100 resources. Business has 60: 40 articles and 20 videos. Daily life has 40: 10 articles and 30 videos. Each resource belongs to exactly one topic and one format in this example.
Business receives 60 / 100 × 360 = 216 degrees of the circle, and Daily life receives 144 degrees. Within Business, articles occupy 40 / 60 = 66.7% of that branch, corresponding to 144 degrees of the complete circle. Business videos occupy the remaining 72 degrees.
Business articles are therefore 66.7% of their parent but 40% of the whole collection. Those percentages answer different questions. The two topic totals sum to 100; their four leaf counts also sum to 100. Adding both levels together would produce 200 and count every resource twice. The calculation assumes inclusive parent totals and a complete, non-overlapping allocation.

Illustrative case study

In a fictional project, Sequoia Learning builds a sunburst for its resource catalog. The first version places resources under every topic tag they carry. The chart's total then exceeds the number of distinct resources, while its title still says “Resources.”
Editors decide that the chart should describe the primary-topic hierarchy. They assign one primary topic per resource and keep optional tags available in a separate view. Tooltips identify the full path, count, percentage of parent and percentage of total. A table gives readers another way to inspect small categories.
The revised display answers a clearer question about the catalog's composition. It does not establish which content readers prefer or which topic deserves more investment. This fictional case illustrates why membership and denominators need clear definitions.

Common misconceptions and mistakes

Do not add parents and descendants as though they were separate contributions when parent values already include their children. Also avoid presenting overlapping tags as a partition of unique items unless the allocation method is explicit.
A small outer sector may be difficult to compare with a distant sector. Many levels and tiny categories can make labels unreadable. Limit detail, support navigation or provide an alternative view when necessary.
Color does not inherently mean performance, and a larger branch does not inherently mean a better result. State the measure and explain any color encoding. Missing classifications should be visible or accounted for, rather than silently excluded from the apparent whole.

Business use

Use a sunburst to explore composition within a meaningful hierarchy, such as a catalog or work breakdown. Start with a question that requires both parent-child relationships and quantities. Verify totals against a simple table before styling the chart.
Provide exact values for decisions that depend on close comparisons. If users drill into a branch, make any change in the displayed denominator clear. Keep an accessible table or text summary alongside the visual so the hierarchy and values remain available without relying on color, small labels or pointer interaction.

Check your understanding

Why are Business articles both 66.7% and 40%?

Answer: The first denominator is Business and the second is the whole collection.

Why not sum every ring?

Answer: Parent and child levels can represent the same items.

When might a bar chart help?

Answer: When accurate comparison of category sizes matters more than showing the hierarchy.

Related terms

Parent node
Pie chart
Aggregation
Data visualization
Hierarchy
leaf node
treemap
icicle chart
part-to-whole comparison

Learn next

Create a small hierarchy and reconcile its leaf totals with its parent totals. Write labels for both percentage-of-parent and percentage-of-total before choosing a visual layout.

Sources

Plotly, Sunburst Charts in Python: hierarchy representation, repeated labels and branch-value examples. https://plotly.com/python/sunburst-charts/ Plotly, Sunburst Trace Reference: value aggregation and percentage-label options. https://plotly.com/python/reference/sunburst/ The resource counts, angle calculations and Sequoia Learning case are original illustrations.

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