This entry is part of the Chart Index, the reference library for the Chart Design Field Guide.

The sunburst is a treemap rolled into a polar coordinate system. Hierarchy goes outward from the centre; each ring is a level of the tree; each arc within a ring is a node whose angular extent is its share of the parent. The form is striking — it visualises hierarchy as a radial wheel — and it shares the treemap's strengths and weaknesses, with angle replacing area as the perceptual encoding.

It is the chart most often used when aesthetics drive form selection. A sunburst on a tile is more eye-catching than a treemap of the same data. The trade-off: angle is harder to compare precisely than area, and the outer rings — where the most leaves live — get the most space per node but lose hierarchical context to the eye.

What it is

A sunburst maps a hierarchical categorical structure to nested arcs in a polar coordinate system. The centre represents the root; each successive ring is a level deeper in the hierarchy. Each arc's angular extent is proportional to its value as a share of its parent. The outermost ring holds the leaves; the inner rings hold the containers.

The hero chart above is a household budget: four categories on the inner ring, seventeen line items on the outer. The first reading is angular — housing is nearly half the wheel, and the mortgage alone is a third of it — and the second is radial: follow any outer arc inward and its category is directly beneath it. Randomise the line items and the categories re-size from their children; the wheel re-divides but never re-orders.

When to use it

Sunbursts are the right choice when:

  • You have a deep hierarchy (3+ levels) and want to show all levels at once.
  • The part-to-whole relationship is the message at every level.
  • The chart will be prominent and large — sunbursts need room to breathe.
  • The audience expects an editorial or eye-catching form — dashboards for executives, public-facing displays.
  • You do not need precise comparison between specific nodes.

When not to use it

  • Precise quantitative comparison. Angle perception is poor; arc-length perception varies with radius. For accurate comparison, use a treemap or bar chart.
  • Very deep hierarchies (5+ levels). Each ring is thinner than the last; the outermost rings become unreadably thin strips.
  • Wide hierarchies at the leaf level. Hundreds of leaves produce a fringe of pixel-wide arcs around the rim. Aggregate or filter.
  • Mixed-sign data. Sunbursts require non-negative values for the part-to-whole semantics.

Design principles

Know what the wheel costs

The sunburst and the treemap draw the same tree. The treemap encodes a leaf as area; the sunburst encodes it as angle, which the eye judges less accurately, and it spends the centre of the frame on the root, which carries no information. The two figures below draw the household budget both ways.

As a sunburst: the shares read as a wheel
Four categories, seventeen line items. Housing's dominance is obvious, and the outer ring makes the mortgage's share of the whole vivid — but ask which is bigger, dining or fuel, and you are comparing two short arcs at the same radius.
As a treemap: the same budget, every dollar a pixel
Identical data. Dining and fuel are now two rectangles whose areas the eye can weigh, every line item has room for its label, and nothing is spent on an empty centre. What is lost is the wheel — the sense of a whole divided.

Limit depth to 3–4 levels

Each additional ring eats radial space. Three levels read cleanly; four are workable; five and beyond are decorative. If the data has more levels, aggregate or use a treemap, which uses space more efficiently. The two figures below draw a project's disk usage at two and then four levels.

Two rings: folders and their largest children
A code checkout with four top-level folders. Two rings leave every arc wide enough to label and the radial thickness generous enough to see the hue shift from parent to child.
Four rings: the same checkout to the file level
Every folder opened two levels further. The outer rings are now slivers, most of their labels are dropped because the arcs are too narrow to hold them, and the hue steps have run out of room to stay distinct — the depth is there, but it is not readable.

Use a hierarchical colour palette

The inner ring gets distinct hues. Each child inherits its parent's hue with a slight lightness or saturation shift — that is how every sunburst on this page is coloured. The reader follows colour to trace a branch from centre to rim. A flat categorical palette across all rings makes the hierarchy invisible.

Label only what fits

Outer-ring leaves often have room for labels; inner rings have less. Set a minimum arc width — the figures here print a label only on arcs wider than 12 degrees — and let the rest go to tooltips. A label squeezed into an arc that cannot hold it spills onto its neighbours and is worse than none.

A wide leaf level: only the arcs that can hold a label get one
Three regions, twenty-two stores. The big stores are labelled; the small ones are not, and the wheel stays clean. Hover any arc for its name and value — a rule for the label, a tooltip for the rest.

Provide tooltips and zoom

Static sunbursts of dense data are hard to read precisely. Interactive sunbursts — hover for the value, click to zoom into a sector — turn the form from a chart into an explorer. For editorial work, design for the static reading first: the hover on every figure here shows the value and its share of the whole, but the arcs must carry the story without it.

Quiet the outermost ring

The leaves tend to dominate visually because they have the most circumference. The hue step that lightens each ring does some of this work; capping the depth at three levels and showing remaining detail in an adjacent panel does the rest.

Avoid the dark centre

A solid filled centre wastes space and adds visual weight. Either leave it empty — the house sunburst does — or use it for a total label or title. The centre is structurally the root, and the root is the whole; it does not need to be painted to be understood.

Show the total

State the total in the subtitle or centre. The sunburst's part-to-whole semantics require a defined whole; without it, the percentages have no anchor.

Anatomy

The composition of a sunburst
An anatomical guide

A sunburst's anatomy is concentric rings of arcs, each ring a hierarchical level, the centre an anchor for the total. The reading task: trace radially from the centre outward to find a leaf in its context, and around the ring to compare siblings.

  • Treemap — the rectangular sibling. More precise, less visually distinctive.
  • Icicle chart — the same partition unrolled into straight bands.
  • Donut chart — degenerate sunburst with one ring.
  • Radial tree — the same polar layout for structure alone, with links instead of arcs.
  • Radial bar chart — bars in polar coordinates; different question (comparison, not hierarchy).

Reading list

  • Stasko, J. & Zhang, E. (2000). Focus+Context Display and Navigation Techniques for Enhancing Radial, Space-Filling Hierarchy Visualizations. The interactive sunburst foundations.
  • Shneiderman, B. (1996). The Eyes Have It: A Task by Data Type Taxonomy for Information Visualizations. The reasoning behind hierarchical displays.
  • Heer, J., Bostock, M. & Ogievetsky, V. (2010). A Tour Through the Visualization Zoo. Sunburst variants and trade-offs.
  • Cleveland, W. & McGill, R. (1984). Graphical Perception. Why angle ranks below length and area.