Venn diagram encodes values as intersection area of overlapping closed curves. John Venn, 1880; Euler drew related region diagrams earlier.
In reports, ads and assignments it fits two or three sets with a real overlap story. Skip it when four-plus sets, or when sizes must be to scale.
Mistakes
- Failure modes 1 — four-plus sets, or when sizes must be to scale
- Failure modes 2 — 3-D pies and perspective bars
- Failure modes 3 — Dual axes that fake a correlation
- Failure modes 4 — Truncated axes that shout a small delta
- Failure modes 5 — Legend only, no direct labels
- Failure modes 6 — Missing source, unit or period
Fixes
- Fixes 1 — Return to two or three sets with a real overlap story.
- Fixes 2 — Flat, one axis, direct labels.
- Fixes 3 — Color-blind-safe palette plus pattern.
- Fixes 4 — Rewrite the title as a claim and add a source line.
Venn diagram: honour intersection area of overlapping closed curves, and switch when four-plus sets, or when sizes must be to scale.