Intermediaterelationship
Heatmap
Encode values as colors in a matrix to reveal patterns across two categorical dimensions.
Quick Facts
Complexity
intermediate
Category
relationship
Heatmap · Example Data
When to use a Heatmap
- Revealing patterns in a matrix of two categorical dimensions
- Calendar/activity data (GitHub contribution graph)
- Correlation matrices between variables
- Website analytics (page × device, hour × day patterns)
About the Heatmap
A heatmap uses color intensity to represent values at the intersection of two categorical (or discretized) axes. It is extremely powerful for revealing patterns, anomalies, and correlations in tabular data at a glance.
Calendar heatmaps (like GitHub's contribution graph) show activity over time. Correlation heatmaps show pairwise variable relationships. The color scale choice critically affects interpretation — use sequential scales for magnitude and diverging scales for positive/negative deviation from center.