Scatterplot Matrix Techniques for Large N

High-performance interaction with scatterplot matrices is a powerful approach to exploratory multivariate data analysis. For a small number of data points, real-time interaction is possible and overplotting is usually not a major problem. When the number of plotted points is large, however, display techniques that deal with overplotting and slow production are important. This article addresses these two problems. Topics include density representation by gray scale or by symbol area, alternatives to brushing, and animation sequences. We also discuss techniques that are generally applicable, including interactive graphical subset selection from any plot in a collection of scatterplots and comparison of scatterplot matrices.