Small multiples, or the science and art of combining graphs

Good graphics often exploit a simple graphical design repeated for different parts of the data, which Edward R. Tufte dubbed the use of small multiples. In Stata small multiples are supported for different subsets of the data through by() or over() options of many graph commands: users can easily emulate that in their own programs by writing wrapper programs that call twoway or graph bar and its siblings. Otherwise specific machinery offers repetition of a design for different variables, such as the (arguably much under-used) graph matrix command. There always remains scope for users to put together their own composite graphs by saving individual graphs and then combining them. The main focus of this presentation is work offering further modest automation of the same design repeated for different data. Three moderately general programs allow small multiples in different ways. sparkline, inspired also by Tufte, but using a centuries-old design popular in many sciences, is most obviously suitable for multiple time series, but has other applications. crossplot offers a simple student-friendly graph matrix but for each y and each x variable specified, so more generally than a scatter plot matrix. combineplot is a more general command for combining univariate or bivariate plots for different variables.