Heatmap
Also called: Heat map, Highlight table, Colour-scale matrix
A heatmap is a grid where each cell is shaded by its value, darker for higher, so patterns across two dimensions, like day of week by hour, stand out before you read a number.
How a heatmap works
A heatmap takes a matrix of one measure across two dimensions and replaces (or backs) each number with a colour. The eye picks out dark blocks long before it reads a single value.
In the example above, the dark band across weekdays from 8:00 to 16:00 tells a support lead where to put staff, and the pale weekend rows tell them where not to. The same 42 numbers as a plain table would take a minute to read.
Types of heatmap
Ordered from most to least common on dashboards:
- Highlight table. A matrix with numbers and shading. The default in business reporting because people still want the figures.
- Time grid. Day by hour or week by weekday, as in the illustration. Great for staffing, traffic and load.
- Calendar heatmap. One cell per day in a calendar layout. Shows weekly rhythm and streaks at a glance.
- Correlation matrix. Every measure against every other, shaded by how strongly they move together. More common in analysis than on dashboards.
Pick the right colour scale
- Sequential (one hue, light to dark) for anything that runs from low to high: counts, revenue, hours.
- Diverging (two hues around a neutral midpoint) for values with a meaningful zero: variance to target, growth, correlation.
Colour follows meaning: if higher is bad, as with complaints or costs, make sure the scale or the caption says so.
In Power BI vs. Tableau
| Power BI | Tableau | |
|---|---|---|
| Built-in | Matrix + conditional formatting (background colour scale) | Heat map and Highlight table in Show Me |
| Colour scale | Gradient or rules in the conditional formatting dialog | Edit Colours on the Colour legend |
Best practices
- Say what darker means. A caption like “Darker = more tickets” turns decoration into information.
- Use bins or a legend so readers can tell 120 from 160.
- Keep it small enough to label, roughly 8 rows by 6 columns. Beyond that, drop the numbers and rely on colour.
- Order rows and columns naturally (Mon → Sun, morning → night), or sort by total so the pattern is easy to see.
Mocking up a heatmap
In Mockko, a heatmap is the matrix visual with a colour scale turned on, plus a caption saying what darker means. Agree the two dimensions and the scale on a mockup before anyone writes the conditional formatting.
