Every ggplot2 plot has three key components:
1. data,
2. A set of aesthetic mappings between variables in the data and visual
properties, and
3. At least one layer which describes how to render each observation. Layers
are usually created with a geom function.
Here’s a simple example:
ggplot(mpg, aes(x = displ, y = hwy)) +
geom_point()