如何在R中的谷歌地图上加入ggplot点？

Question

I know how to join points using ggplot():

dd <- data.frame(a=c(21.01223,18.45598,17.04542,19.44312),b=c(52.22968,51.75925,50.12482, 51.78745),
                 g=rep(1:2,2))

library(ggplot)

ggplot(data=dd,aes(x=a,y=b,group=g)) +
  geom_point(col=rep(c("darkred","black"),each=2),size=5)+
  geom_line(linetype=3)

but how to join this points on google map ? I can only draw the points, but how to join them ?

library(ggmap)
qmap('Poland',zoom=6) + 
geom_point(data=dd,aes(x=a,y=b),col=rep(c("darkred","black"),each=2),size=5)

Answer 1

To join the points you can pass the data into the geom_line() geom as well.

library(ggmap)
myMap <- get_map("Poland", zoom = 6)

ggmap(myMap) + 
  geom_point(data=dd, aes(x=a,y=b), col=rep(c("darkred","black"), each=2), size=5) +
  geom_line(data=dd, aes(x=a, y=b, group = g))