Graphical Parameters and Other Settings

In the second part of this book, we take a detailed look at features that are common to all high-level lattice functions, providing a uniform interface to control their output. We start, in this chapter, by describing the system of user settable graphical parameters and other global options.

Graphical parameters are often critical in determining the effectiveness of a plot. Such parameters include obvious ones such as colors, symbols, line types, and fonts for the various elements of a graph, as well as more subtle ones such as the length of tick marks or the amount of space separating different components of the graph. The parameters used in lattice displays are highly customizable. Many of them can be controlled directly by specifying suitable arguments in a high-level function call. Most derive their default values from a system of common global settings that can also be modified by the user. The latter approach has two primary benefits: it allows good global defaults to be specified, and it provides a consistent “look and feel” to lattice graphics while letting the user retain ultimate control.

Not all parameters of interest are graphical. For example, a user may dislike the default argument value as.table = FALSE (which orders panels starting from the lower-left corner rather than the upper-left one), and wish to change the default globally rather than specify an additional argument in every call. Several such non-graphical parameters can be customized, through a slightly different system of global options. Both these systems are discussed in this chapter.