[R-sig-Geo] White space in maps library

[Brian J. Lopes]

Hey All,

I have a quick question regarding the maps package, and I'm not sure 
what I'm missing.

Let's say I just want a plot of the US, by using the world data and to 
save it as a png

library(maps)
png("test.png")
map('world', xlim=c(-125,-50),ylim=c(25,50))
map.axes()
dev.off()

The limits are actually important for me, so that's why I'm not using 
'usa'.  As you can see by looking at the png file, there is a lot of 
excess white space both above and below the file, I guess this has to do 
with the dimensions of the png file, but setting the dimensions in the 
png() function doesn't seem to help the matter.

Any advice on how to deal with this?

TIA,
Brian