Taxonomy of Data Visualization Methods - Data Visualization: A Successful Design Process - page 140

Scatter plot matrix
Data variables : 2 x quantitative, 2 x categorical.
Visual variables : Position, color-hue.
Description : Similar to the small multiples chart that we saw earlier, a scatter plot
matrix takes advantage of the eye's rapid capability to spot patterns across multiple
views of the same type of chart. In the following case, we have a panel of multiple
combined scatter plots:
Image from "Scatterplot Matrix" ( http://mbostock.github.com/d3/ex/splom.html ),
created by Mike Bostock
Heatmap (or matrix chart)
Data variables : Multiple x categorical, 1 x quantitative-ratio.
Visual variables : Position, color-saturation.