US.r
"US" <-
function (xlim = c(-124.7, -67.1), ylim = c(25.2, 49.4), add = FALSE,
shift=FALSE, ...)
{
if (!exists("US.dat"))
data(US.dat)
if( shift){
US.dat$x[ US.dat$x<0] <- US.dat$x[ US.dat$x<0] +360}
if (!add) {
plot(US.dat$x, US.dat$y, ylim = ylim, xlim = xlim, xlab = "",
ylab = "", type = "n", xaxt = "n", yaxt = "n", ...)
}
lines(US.dat$x, US.dat$y, err = -1, ...)
invisible()
}