library(maps);
library(ggplot2);
# Get US map
usa <- map_data("state");
myData = data.frame(name=c("FL","CO","CA","MA","NY"),
lat=c(29,39,38,42,43),
long=c(-82,-105,-120,-71,-75),
pop=c(19.3,5.2,38.0,6.6,19.6))
ggplot() +
geom_path(data = usa, aes(x=long, y=lat, group = group)) +
geom_point(data = myData, aes(x=long, y=lat, size=pop),
color = "red");