世界地图：

library(maps)data("world.cities")bigcities <- subset(world.cities, pop > 5000000)qplot(long, lat, data = bigcities,colour=country.etc,size=pop)+ borders("world", size= 0.5)

中国地图：

library(mapdata)ch_cities <- subset(world.cities, country.etc=="China")ggplot(ch_cities, aes(long, lat)) + geom_point(colour= alpha("red",0.5))+ borders("china")#

合并数据到地图数据：

　　

states <- map_data("state")##将地图数据转为数据框arrests <- USArrests ##新数据（要与地图数据中的某一列匹配）names(arrests) <- tolower(names(arrests)) ##将列名翻译为小写，因为state数据的region为小写arrests$region <- tolower(rownames(USArrests)) ##增添新列 regionchoro <- merge(states, arrests, by = "region")# Reorder the rows because order matters when drawing polygons# and merge destroys the original orderingchoro <- choro[order(choro$order), ]qplot(long, lat, data = choro, group = group,   fill = Assault, geom = "polygon") ##多边形qplot(long, lat, data = choro, group = group,   fill = Assault / murder, geom = "polygon")ia <- map_data("county", "iowa")library(plyr)mid_range <- function(x) mean(range(x, na.rm = TRUE))centres <- ddply(ia, .(subregion),   colwise(mid_range, .(lat, long)))  ##计算区的中心位置ggplot(ia, aes(long, lat)) +   geom_polygon(aes(group = group),     fill = NA, colour = "grey60") +  geom_text(aes(label = subregion), data = centres,  ##对地图标注    size = 2, angle = 45)出现问题时：dev.off()