I'm learning how to use ggplot2 and would like to make a graph and then overlap a point in it. For example:
set.seed(1)
a = data.frame(X1 = rnorm(3), X2 = rnorm(3))
g <- ggplot(a, aes(x = X1, y = X2), colour="black", fill = NA) + geom_polygon()
ponto = c(-.4, .5)
Thank you in advance!