Fundamentals of Data Visualization

Chapter 21. Multipanel Figures

When datasets become large and complex, they often contain much more information than can reasonably be shown in a single figure panel. To visualize such datasets, it can be helpful to create multipanel figures. These are figures that consist of multiple figure panels where each one shows some subset of the data. There are two distinct categories of such figures, small multiples and compound figures. Small multiples are plots consisting of multiple panels arranged in a regular grid. Each panel shows a different subset of the data but all panels use the same type of visualization. Compound figures consist of separate figure panels assembled in an arbitrary arrangement (which may or may not be grid-based) and showing entirely different visualizations, or possibly even different datasets.

We have encountered both types of multipanel figures in many places throughout this book. In general, these figures are intuitive and straightforward to interpret. However, when preparing such figures, there are a few issues we need to pay attention to, such as appropriate axis scaling, alignment, and consistency between separate panels.

Small Multiples

The term “small multiple” was popularized by [Tufte 1990]. An alternative term, “trellis plot,” was popularized around the same time by Cleveland, Becker, and colleagues at Bell Labs ([Cleveland 1993]; [Becker, Cleveland, and Shyu 1996]). Regardless of the terminology, the key idea is to slice the data into parts according ...