9.6 Bubble Charts

• A bubble chart is basically just a scatterplot where the point size is proportional to the values of a third quantitative variable.

• Bubble charts are quite popular but controversial for the same reason that pie charts are controversial, the fact that people are better at judging length than volume.

• Here we use the mtcars dataset to plot car weight vs. mileage and use point size to represent horsepower.

data(mtcars)
library(ggplot2)
ggplot(mtcars, aes(x = wt, y = mpg, size = hp)) +
  geom_point()