Scatter Plot or Heatmap: A Decision Guide for Dense Data
Both show relationships between two variables. They are not interchangeable. Learn when each one is the right choice.
Scatter plots and heatmaps both encode two variables against each other. Despite that overlap, they answer different questions, and using the wrong one is the fastest way to confuse a reviewer.
Use a scatter plot when individual data points matter. Outliers, clusters, and linearity are all easier to read when each observation is its own dot. If your reviewer will care about which specific points drive the effect, scatter wins.
Use a heatmap when individual points stop mattering and density does. Once you have more than about 1,500 points, a scatter plot becomes an inky blob that hides the pattern it is supposed to reveal. A two dimensional binned heatmap recovers the structure.
Avoid heatmaps when the axes are not comparable in scale. If X is time and Y is category count, a heatmap cell implies a relationship that the data does not support. Use a grouped bar chart instead.
Chart Builder offers both and lets you switch between them without rebuilding the dataset. When in doubt, try both. The right choice is usually obvious within fifteen seconds.