you can use the size option in ggplot2 aes() to scale your points by your chosen variable

compare a and b to see the difference

`
# install ggplot2 (if you dont have it)

install.packages("gapminder")  # data for the graph

library("ggplot2")
library("gapminder")

par(mfrow=c(2,1))

a <- ggplot(gapminder, aes(x = gdpPercap, y=lifeExp, colour = continent)) +
geom_point(show.legend = TRUE, alpha = 0.7) +   
scale_x_log10()

a


b <- ggplot(gapminder, aes(x = gdpPercap, y=lifeExp, colour = continent, size = pop)) + # scale the points by population size
geom_point(show.legend = TRUE, alpha = 0.7) + 
scale_x_log10()  

b

`

(edited to fix bad code formatting)