grid Graphics
Paul Murrell
April 17, 2009
grid is a low-level graphics system which provides a great deal of control and flexibility in the
app earance and arrangement of graphical output. grid does not provide high-level functions
which create complete plots. What it does provide is a basis for developing such high-
level functions (e.g., the lattice package), the facilities for customising and manipulating
lattice output, the ability to produce high-level plots or non-statistical images from scratch,
and the ability to add sophisticated annotations to the output from base graphics functions
(see the gridBase package).
This document provides an introduction to the fundamental concepts underlying the grid
package: viewports, units, and graphical parameters. There are also several examples
to demonstrate what can be achieved and how to achieve it.
The description of the fundamental grid concepts is predicated on the following approach
to constructing a statistical graphic (plot). You must be able to:
1. create and control different graphical regions and coordinate systems.
2. control which graphical region and coordinate system graphical output goes into.
3. produce graphical output (lines, points, text, ...) including controlling its appearance
(colour, line type, line width, ...).
1 Creating and Controlling Graphics Regions and Co-
ordinate Systems
In grid there can be any number of graphics regions. A graphics region is referred to as
a viewport and is created using the viewport() function. A viewport can be positioned
anywhere on a graphics device (page, window, ...), it can be rotated, and it can be clipped
to. The following code describes a viewport which is centred within the page, and is half the
width of the page, one quarter of the height of the page, and rotated 45
◦
; Figure 1 shows a
diagram of this viewport.
> viewport(x = 0.5, y = 0.5, width = 0.5, height = 0.25,
+ angle = 45)
1
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