I have another post in my ggplot2 series:
Annotations are useful for marking out important comments in your visual. For example, going back to our wealth and longevity chart, there was a group of Asian countries with extremely high GDP but relatively low average life expectancy. I’d like to call out that section of the visual and will use an annotation to do so. To do this, I use the annotate() function. In this case, I’m going to create a text annotation as well as a rectangle annotation so you can see exactly the points I mean.
By this point, we’re getting closer and closer to high-quality graphics.