Small multiples (also called trellis charts or lattice charts) provide data visualization of many small, interrelated graphs clustered together in a single display. This layout makes it easy to compare different aspects of the same large data set. Rather than having one chart with many overlapping and potentially confusing variables, each small chart focuses on a few easily digested pieces of information. With this approach, the user need only review the chart labels and legends briefly to grasp the overall meaning of the data presented throughout the series. For certain data sets, the use of small multiples reduces the mental processing required to understand the data presented.
The charts may be arranged sequentially to show changes over time. Or, they may be used to demonstrate another variable as the charts are scanned as a group. For example, the basic chart may be a map of the United States. Each small chart in the multiple set might highlight states based on average population age, income, political affiliation, or other demographic information. Typically, only two variables are used in charts featured as small multiples. Otherwise, the charts become too difficult to analyze visually. For best results, each chart is identical in format and has at least one common variable with all the other charts in the series. Each one is simply populated with a different slice of data.