9.2 Changing the Appearance of Text

9.2.1 Problem

You want to change the appearance of text in a plot.

9.2.2 Solution

To set the appearance of theme items such as the title, axis labels, and axis tick marks, use theme() and set the item with element_text(). For example, axis.title.x controls the appearance of the x-axis label and plot.title controls the appearance of the title text (Figure 9.4):

library(gcookbook)  # Load gcookbook for the heightweight data set

# Base plot
hw_plot <- ggplot(heightweight, aes(x = ageYear, y = heightIn)) +
  geom_point()

# Controlling appearance of theme items
hw_plot +
  theme(axis.title.x = element_text(
    size = 16, lineheight = .9,
    family = "Times", face = "bold.italic", colour = "red"
  ))

hw_plot +
  ggtitle("Age and Height\nof Schoolchildren") +
  theme(plot.title = element_text(
    size = rel(1.5), lineheight = .9,
    family = "Times", face = "bold.italic", colour = "red"
  ))

# rel(1.5) means that the font will be 1.5 times the base font size of the theme.
# For theme elements, font size is in points.

Figure 9.4: axis.title.x (left); plot.title (right)

To set the appearance of text geoms (text that’s in the plot itself, with geom_text() or annotate()), set the text properties. For example (Figure 9.5):

hw_plot +
  annotate("text", x = 15, y = 53, label = "Some text",
    size = 7, family = "Times", fontface = "bold.italic", colour = "red")

hw_plot +
  geom_text(aes(label = weightLb), size = 4, family = "Times", colour = "red")

# For text geoms, font size is in mm

Figure 9.5: annotate("text") (left); geom_text() (right)

9.2.3 Discussion

There are two kinds of text items in ggplot2: theme elements and text geoms. Theme elements are all the non-data elements in the plot: the title, legends, and axes. Text geoms are things that are part of the plot itself, and reflect the data content.

There are differences in the parameters, as shown in Table 9.1.

Table 9.1: Text properties of theme elements and text geoms

Theme elements	Text geoms	Description
family	family	Helvetica, Times, Courier
face	fontface	plain, bold, italic, bold.italic
colour	colour	Color (name or “#RRGGBB”)
size	size	Font size (in points for theme elements; in mm for geoms)
hjust	hjust	Horizontal alignment: 0 = left, 0.5 = center, 1 = right
vjust	vjust	Vertical alignment: 0 = bottom, 0.5 = middle, 1 = top
angle	angle	Angle in degrees
lineheight	lineheight	Line spacing multiplier

The theme elements are listed in Table 9.2. Most of them are straightforward. Some are shown in Figure 9.6.

Table 9.2: Theme items that control text appearance in theme()

Element name	Description
axis.title	Appearance of axis labels on both axes
axis.title.x	Appearance of x-axis label
axis.title.y	Appearance of y-axis label
axis.ticks	Appearance of tick labels on both axes
axis.ticks.x	Appearance of x tick labels
axis.ticks.y	Appearance of y tick labels
legend.title	Appearance of legend title
legend.text	Appearance of legend items
plot.title	Appearance of overall plot title
strip.text	Appearance of facet labels in both directions
strip.text.x	Appearance of horizontal facet labels
strip.text.y	Appearance of vertical facet labels

Figure 9.6: Aligning with hjust and vjust, and spacing with lineheight