Chart Type for Hierarchical Proportional. Keywords: sunburst, hierarchy, nested, proportion, radial, circle. Best Chart: Sunburst Chart. Secondary Options: Treemap, Icicle, Circle Packing. When to Use: Exploring nested proportions where both hierarchy and relative size matter (e.g., org spend breakdown). When NOT to Use: More than 3 hierarchy levels (outer rings become unreadable); precision matters over overview; mobile. Data Volume Threshold: <100 nodes: SVG; 100–500: Canvas; >500: filter to top N before rendering. Color Guidance: Center to outer: darker to lighter hue. Each level 15–20% lighter. Contrasting border between sectors. Accessibility: C — Poor accessibility beyond 2 levels. Mandatory table alternative required for any production use.. A11y Fallback: Collapsible indented list with percentages; breadcrumb trail for current drill-down state. Library: D3.js (d3-hierarchy), Recharts, ApexCharts. Interactive Level: Drilldown + Hover.