Relationship
Heatmap
- Relationship
What it shows
Values as colour across a grid.
When to use it
Use it when
Spotting patterns across two categories, such as day and hour.
Avoid it when
Readers need exact values.
When to use it
Use a heatmap to show an intensity measure across two ordered or categorical dimensions.
Worked example
Plot support tickets by hour of day and weekday. If staffing differs across hours, tickets per staffed hour may be more comparable than raw ticket counts.
Data required
Two dimensions, an intensity measure, the denominator where relevant and a consistent colour scale.
Checks and common mistakes
Use a legend and a perceptually ordered palette. Flag missing cells and annotate important values; colour alone cannot convey exact amounts.
More accessible alternative
A labelled matrix or small multiples can be clearer for a few categories.