Click any arc to zoom in · Click centre to zoom out · Arc angle ∝ value
A sunburst diagram encodes a hierarchy as a series of concentric rings. The centre circle is the root node. Each ring outward represents one level deeper in the hierarchy. Within each ring, arcs are sliced proportionally to a numeric value — arc angle and arc length encode magnitude. The viewer's visual system simultaneously reads containment (which node belongs to which parent, conveyed by angular alignment) and proportion (how much each node contributes to its parent, conveyed by arc angle).
This dual encoding — hierarchy structure plus proportional composition — is the sunburst's unique capability. No other chart type conveys both in a single view without requiring the reader to cross-reference between two separate charts.
When arcs are divided equally under a parent, the chart emphasises hierarchy structure — every child node gets equal visual weight regardless of its value. This is useful when the branching pattern itself is the message. When arcs are proportional to a value (as implemented here), the chart emphasises composition — each node's arc angle represents its share of the parent's total. The choice between these modes is a design decision that depends on whether structural equality or magnitude comparison is the message.
The data structure is a three-level hierarchy with numeric leaf values: industry → company → product line → revenue. The message is compositional at every level simultaneously: which industry dominates, which company dominates within each industry, and which product line drives each company. A treemap would answer the same question but loses the explicit parent–child ring structure that makes the hierarchy legible. A pie chart can only show one level. The sunburst shows all levels at once with a single glance.
A treemap — the nearest alternative — packs all leaf nodes into rectangular area without showing the intermediate branch levels as visible elements. It is better for precise area comparison of leaf nodes; worse for communicating the hierarchical grouping structure. A nested pie chart (multiple concentric pies) is perceptually equivalent but harder to implement cleanly because it requires manual ring sizing. The sunburst's continuous angle encoding makes parent–child proportional relationships clearer than separate concentric pies.
The sunburst performs poorly when the hierarchy is very deep (more than four rings), when many nodes at one level have very small values (thin slivers become unreadable), or when the message is precise comparison rather than structural overview. In those cases, a hierarchical bar chart or treemap is more appropriate.
The click-to-zoom interaction is not a navigation convenience — it is an analytical necessity. A sunburst with four or more levels and many nodes becomes visually dense at full scale. Zooming into a branch re-partitions the full angular space to show only that subtree's children, making small arcs readable. The breadcrumb trail above the chart preserves the viewer's positional context within the hierarchy — without it, zoom interactions disorient the reader. These two elements are inseparable.
FT Visual Vocabulary category: Part-to-whole — "How a single entity is made up of its components." Abela quadrant: Composition (hierarchical, accumulating over levels). Tufte principle: the rings are data (hierarchy levels); the arcs are data (proportional values); the angular alignment of parent and children arcs is data (containment relationship). The only non-data ink is the thin white stroke separating arcs — necessary for figure–ground separation between adjacent slices.