Annotate outside plot area once in ggplot with facets

Question

I want to add an annotation outside the plotting area in a faceted ggplot. I can get the annotation that I want, but it\'s repeated for each facet. How can I get this annota

Answer 1

You can put a single tag label on a graph using tag in labs().

ggplot(mtcars, aes(x = hp, y = mpg)) +
     geom_point() +
     facet_grid(.~cyl ) + 
     labs(tag = "XX") +
     coord_cartesian(xlim = c(50, 350), ylim = c(10, 35), clip = "off")

This defaults to "top left", though, which may not be what you want. You can move it around with the theme element plot.tag.position, either as coordinates (between 0 and 1 to be in plot space) or as a string like "topright".

ggplot(mtcars, aes(x = hp, y = mpg)) +
     geom_point() +
     facet_grid(.~cyl ) + 
     labs(tag = "XX") +
     coord_cartesian(xlim = c(50, 350), ylim = c(10, 35), clip = "off") +
     theme(plot.tag.position = c(.01, .95))