使用qmplot在地图中指向

Question

I have to plot some points in a map. I want to use qmplot , because it seems simple and effective.

I have followed this tutorial , but I cannot get it to work:

# Libraries
install.packages("maps")
install.packages("ggmap")
library(maps)
library(ggmap)

# Loading European map:     
map <- get_map(location = 'Europe', zoom = 4)
ggmap(map)

# Madrid coordinates
df <- data.frame(lon=c(-3.757324), lat=c(40.441721))

# Plotting the point
qmplot(df$lon, df$lat)
qmplot(df$lon, df$lat, data = df)

I get this error:

Error in `[.data.frame`(data, , deparse(substitute(x))) :
undefined columns selected

Answer 1

If you want to draw your points over the map of Europe you get in the first step, this is what you can do instead:

# Libraries
library(maps)
library(ggmap)

# Loading European map:     
map <- get_map(location = 'Europe', zoom = 4)

# Madrid coordinates
df <- data.frame(lon=c(-3.757324), lat=c(40.441721))

ggmap(map) + geom_point(data = df, aes(x = lon, y = lat))