Chapter 7. Annotations

Displaying just your data usually isn’t enough—there’s all sorts of other information that can help the viewer interpret the data. In addition to the standard repertoire of axis labels, tick marks, and legends, you can also add individual graphical or text elements to your plot. These can be used to add extra contextual information, highlight an area of the plot, or add some descriptive text about the data.

Adding Text Annotations

Problem

You want to add a text annotation to a plot.

Solution

Use annotate() and a text geom (Figure 7-1):

p <- ggplot(faithful, aes(x=eruptions, y=waiting)) + geom_point()

p + annotate("text", x=3, y=48, label="Group 1") +
    annotate("text", x=4.5, y=66, label="Group 2")
Text annotations
Figure 7-1. Text annotations

Discussion

The annotate() function can be used to add any type of geometric object. In this case, we used geom="text".

Other text properties can be specified, as shown in Figure 7-2:

p + annotate("text", x=3, y=48, label="Group 1", family="serif",
             fontface="italic", colour="darkred", size=3) +
    annotate("text", x=4.5, y=66, label="Group 2", family="serif",
             fontface="italic", colour="darkred", size=3)
Modified text properties
Figure 7-2. Modified text properties

Be careful not to use geom_text() when you want to add individual text objects. While annotate(geom="text") will add a ...

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