Chart Type for Hierarchical / Nested Data. Keywords: hierarchy, nested, treemap, parent, children, breakdown, drill. Best Chart: Treemap. Secondary Options: Sunburst, Nested Donut, Icicle. When to Use: Showing size relationships within a hierarchy; overview of proportional structure (e.g., budget breakdown). When NOT to Use: Hierarchy depth > 3 levels (too complex to read); user needs to compare sibling values precisely. Data Volume Threshold: <200 nodes: SVG; 200–1000: Canvas; >1000: paginate or pre-filter before rendering. Color Guidance: Parent nodes: distinct hues. Children: lighter shades of same hue. White separator borders: 2–3px. Accessibility: C — Poor baseline accessibility. Always provide table alternative as primary view. Label all large areas.. A11y Fallback: Collapsible tree table as primary view; treemap as supplementary visual only. Library: D3.js, Recharts, ApexCharts. Interactive Level: Hover + Drilldown.