Chart - Heatmap.

Best for: Ops/support peak-time analysis, regional revenue density summaries, weekday x hour activity pattern diagnostics, product usage pattern diagnostics

Use: When row x column intersection data needs to be read at a glance via color intensity. Cohort retention, weekday x time-of-day activity density, region x product revenue density.

Avoid: When comparing 2 entities across multiple dimensions (use radar chart) or placing a few qualitative risk items (use risk matrix), or when axes are fewer than 3 or too many. Use chart-cohort-retention-triangle when the number of filled cells differs per row, as in per-cohort retention by elapsed period; this heatmap is only for a fully populated symmetric cross-tab.