Chart type · Trend
Matrix heatmap
How to read it
Position picks the cell and colour carries the value, so read the legend before the grid. A scanner sweeps the columns, a ring hops between the runner-up cells and locks on the one the clip is about, and its row and column stay lit while the rest dims. In a before/after grid the cells turn to the new values smallest change first, so the biggest mover lands last. In stripes a playhead walks the years with a live reading.
Best for
Two-dimensional patterns, seasonality, streaks, how a grid changed between two dates, and long runs of a single measure.
When not to use it
Exact values matter, or the measure diverges around a midpoint but the ramp runs through a single hue.
The common mistake
A rainbow scale. It invents boundaries the data does not have and falls apart for colour-blind viewers. A close second: comparing two grids on separate colour scales, where an unchanged cell still changes colour.
Example data
When the world is actually awake
Relative app activity by weekday and hour
| Row | 6am | 9am | 12pm | 3pm | 6pm | 9pm | 12am |
|---|---|---|---|---|---|---|---|
| Monday | 18 | 62 | 71 | 68 | 84 | 92 | 41 |
| Tuesday | 19 | 63 | 72 | 69 | 85 | 93 | 42 |
| Wednesday | 20 | 64 | 73 | 70 | 86 | 94 | 43 |
| Thursday | 20 | 63 | 72 | 71 | 88 | 95 | 47 |
| Friday | 19 | 58 | 69 | 72 | 91 | 99 | 66 |
| Saturday | 11 | 34 | 58 | 74 | 88 | 96 | 71 |
| Sunday | 9 | 31 | 55 | 66 | 79 | 87 | 38 |
Stronger colour is higher: 9 to 99. Hover or tab through the cells to read them.
The sample dataset this format ships with, drawn the way the site draws every clip's numbers — hover, sort or step through it. Figures as given by its source line: Illustrative example data.
Examples
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Related chart types
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