I'm brand new to the map function too, here's my attempt at coloring a map of
the states according to a rate (rather than count):
map('state')$names
MyCount <- c(1:63); MyRate <- runif(63, 0, 1)
map('state', fill=TRUE, col=rgb((1-MyRate),MyRate,0,1))
Seeing that there are 63 "states", means you'll have to adjust your data to
fit. For example, look at Washington. I think the effect of MyRate on
color is that as it approaches 1, rgb produces green, and as it approaches
0, rgb produces red. I know you were asking for counts, but I just had this
handy, and I'm learning too. Cheers.