9.7 Modified Bubble Chart

ggplot(mtcars, aes(x = wt, y = mpg, size = hp)) +
  geom_point(alpha = .5, 
             fill="cornflowerblue", 
             color="black", 
             shape=21) +
  scale_size_continuous(range = c(1, 14)) +
  labs(title = "Auto mileage by weight and horsepower",
       subtitle = "Motor Trend US Magazine (1973-74 models)",
       x = "Weight (1000 lbs)",
       y = "Miles/(US) gallon",
       size = "Gross horsepower") 

• The range parameter in the scale_size_continuous function specifies the minimum and maximum size of the plotting symbol. The default is range = c(1, 6).

• The shape option in the geom_point function specifies an circle with a border color and fill color.

• From the graph, generally we see that miles per gallon decreases with increased car weight and horsepower.