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

An icicle chart lays a hierarchy into adjacent rectangular bands. Each level occupies a consistent depth, while the width or height of each node represents the total value of its descendants. It makes hierarchy depth easier to trace than a treemap.

What it is

The root begins at one edge and each generation extends into the next band. Children partition their parent's span, so the chart preserves both containment and part-to-whole magnitude.

When to use it

  • Readers need to trace paths through a hierarchy.
  • Depth is analytically meaningful.
  • Values add from children to parents.
  • Interactive zoom or drill-down will help readers inspect dense branches.

When not to use it

  • Only leaf size matters. A treemap uses the available area more efficiently.
  • The hierarchy is shallow and simple; a tree diagram may be clearer.
  • Values do not aggregate meaningfully through the hierarchy.

Design principles

Keep depth direction consistent

Choose left-to-right or top-to-bottom and preserve it across related views. Direction tells the reader how to traverse the hierarchy.

Use gaps to reveal parent boundaries

Small gaps between siblings clarify grouping. Large gaps waste the span that communicates value.

Label the upper levels first

Parents orient the reader. Hide labels in narrow leaves and provide them through interaction.

Support zoom without losing context

Show the selected path or breadcrumb after zooming so users know where they are in the hierarchy.

Anatomy

Bands represent depth, each node's span represents aggregate value, adjacency shows siblings, and containment is expressed by aligned partitions across levels.

  • Treemap - space-filling hierarchy optimised for leaf area.
  • Sunburst - a radial partition of the same hierarchical structure.
  • Tree - explicit links between parent and child nodes.

Reading list

  • Nivo Icicle documentation - orientation, zooming, and node configuration.
  • Kruskal, J. B. and Landwehr, J. M. (1983). Icicle Plots: Better Displays for Hierarchical Clustering.