Darker cells mean a higher score for this topic on that metric.
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Last reviewed Sources & creditsMedia creditsMethodology
Quick answers
When should I pick Heatmap?
When the story is: patterns across two categorical axes at once.
When should I avoid Heatmap?
Skip it in cases like: precise lookup of a number, or a rainbow that is not color-blind safe.
Who invented or popularised it?
Toussaint Loua’s 1873 crime tables; later Toussaint/Bertin and 1990s gene arrays
What does it encode?
color value of a cell in a row-column grid
Is it OK in ads?
Yes if one claim is visible at a glance in Meta, Google and retail print; otherwise link to a full figure.
Will a teacher accept it?
Yes for lab reports and poster boards if axes, units and a source line are present.
Heatmap encodes values as color value of a cell in a row-column grid. Toussaint Loua’s 1873 crime tables; later Toussaint/Bertin and 1990s gene arrays.
In reports, ads and assignments it fits patterns across two categorical axes at once. Skip it when precise lookup of a number, or a rainbow that is not color-blind safe.
Mistakes
- Failure modes 1 — precise lookup of a number, or a rainbow that is not color-blind safe
- 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 patterns across two categorical axes at once.
- 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.
Heatmap: honour color value of a cell in a row-column grid, and switch when precise lookup of a number, or a rainbow that is not color-blind safe.