Scatter Plots - R Graphics - page 137

Figure 5-30. Left: a scatter plot with manually labeled points; right: with automatically labeled
points and a smaller font
To automatically add the labels from your data ( Figure 5-30 , right), use geom_text() and map
a column that is a factor or character vector to the label aesthetic. In this case, we'll use Name ,
and we'll make the font slightly smaller to reduce crowding. The default value for size is 5,
which doesn't correspond directly to a point size:
sp + geom_text(aes(label = Name), size = 4 )
Discussion
The automatic method for placing annotations centers each annotation on the xand ycoordin-
ates. You'll probably want to shift the text vertically, horizontally, or both.
Setting vjust=0 will make the baseline of the text on the same level as the point ( Figure 5-31 ,
left), and setting vjust=1 will make the top of the text level with the point. This usually isn't
enough, though—you can either increase or decrease vjust to shift the labels higher or lower,
or you can add or subtract a bit to or from the y mapping to get the same effect ( Figure 5-31 ,
right):
sp + geom_text(aes(label = Name), size = 4 , vjust = 0 )
# Add a little extra to y
sp + geom_text(aes(y = infmortality + .1 , label = Name), size = 4 , vjust = 0 )