Create balloon plot with ggplot2: use ..count.. to adjust size of geom_point?

Question

I want to essentially create a balloon plot with ggplot2 where the size of the points are the frequency of data at a given coordinate.

Given the data.frame

Answer 1

Per @BenBolker's suggestion, I found a solution using stat_sum():

ggplot(d, aes(value.x, value.y, size = ..n..)) + stat_sum()