Plot (fill color) map with USA states data in R

问题:

I have following data which I want to plot on States map of the USA:

x = data.frame(state.x77[,"Income"])

How can I plot these as color fill in states on a map?

I can plot the map:

map("state", boundary=TRUE, col=colorRampPalette(c("blue","green","yellow","red"))(50), fill=T)

I can match the states:

match(map("state",plot=F)$names, tolower(rownames(x)))

I tried to modify example from ?map_data :

if (require("maps")) {
states <- map_data("state")
arrests <- USArrests
names(arrests) <- tolower(names(arrests))
arrests$region <- tolower(rownames(USArrests))

choro <- merge(states, arrests, sort = FALSE, by = "region")
choro <- choro[order(choro$order), ]
qplot(long, lat, data = choro, group = group, fill = assault,
  geom = "polygon")
qplot(long, lat, data = choro, group = group, fill = assault / murder,
  geom = "polygon")
}

But I am not able to adjust it. Thanks for your help.

回答1:

You don't need to merge your arrests data with your map data. You can pass the map data separately to a geom_map layer. Try

x = data.frame(region=tolower(rownames(state.x77)), 
    income=state.x77[,"Income"], 
    stringsAsFactors=F)

states_map <- map_data("state")
ggplot(x, aes(map_id = region)) + 
    geom_map(aes(fill = income), map = states_map) +
    scale_fill_gradientn(colours=c("blue","green","yellow","red")) + 
    expand_limits(x = states_map$long, y = states_map$lat)