Create a layer of map borders

This is a quick and dirty way to get map data (from the maps package) on to your plot. This is a good place to start if you need some crude reference lines, but you'll typically want something more sophisticated for communication graphics.

borders(database = "world", regions = ".", fill = NA, colour = "grey50",
  xlim = NULL, ylim = NULL, ...)

Arguments

database	map data, see map for details
regions	map region
fill	fill colour
colour	border colour
xlim, ylim	latitudinal and logitudinal range for extracting map polygons, see map for details.
...	other arguments passed onto geom_polygon

Examples

if (require("maps")) {

ia <- map_data("county", "iowa")
mid_range <- function(x) mean(range(x))
seats <- plyr::ddply(ia, "subregion", plyr::colwise(mid_range, c("lat", "long")))
ggplot(ia, aes(long, lat)) +
  geom_polygon(aes(group = group), fill = NA, colour = "grey60") +
  geom_text(aes(label = subregion), data = seats, size = 2, angle = 45)

data(us.cities)
capitals <- subset(us.cities, capital == 2)
ggplot(capitals, aes(long, lat)) +
  borders("state") +
  geom_point(aes(size = pop)) +
  scale_size_area() +
  coord_quickmap()

# Same map, with some world context
ggplot(capitals, aes(long, lat)) +
  borders("world", xlim = c(-130, -60), ylim = c(20, 50)) +
  geom_point(aes(size = pop)) +
  scale_size_area() +
  coord_quickmap()
}