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.
Use when
- Use when 1 — patterns across two categorical axes at once
- Use when 2 — Excel or Google Sheets
- Use when 3 — PowerPoint
- Use when 4 — lab reports and poster boards
- Use when 5 — Meta, Google and retail print
Avoid when
- Avoid when 1 — precise lookup of a number, or a rainbow that is not color-blind safe
- Avoid when 2 — 3-D, dual axes, rainbow scales
- Avoid when 3 — Undated numbers, undated time series
- Avoid when 4 — Four charts on one slide
Audiences
- Work — PowerPoint
- Ads — Meta, Google and retail print
- School — lab reports and poster boards
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.