如何用ggmap绘制R中地图上的箭头

Question

我试图在R中绘制一个地理图，其中包含各个机场的点，然后在它们之间使用箭头，指示特定的飞行路线。

根据前面关于堆栈溢出的一些问题，使用ggmap和geom_segment应该可以做到这一点，但是使用我在下面代码中使用的方法似乎无法工作：

library(htmlwidgets)
library(leaflet)
library(ggmap)


#=============================== Data ===============================#  


#Retrieving coordinates for two airports
Adress = c("Lufthavnsboulevarden 6, 2770 Kastrup, Denmark", "Edvard Munchs veg, 2061 Gardermoen, Norway")

# This function geocodes a location (find latitude and longitude) using the Google Maps API
geo <- geocode(location = Adress, output="latlon", source="google")

#moving the data around, so that second observation will be end-destination
geo$lonend[1] <- geo$lon[2]
geo$latend[1] <- geo$lat[2]

#removing second row
row_to_keep = c(TRUE, FALSE)
geo = geo[row_to_keep,]

#putting a number in there to make some dots for the airports
geo$Number = 999

#=============================== Ploting =============================# 

# get a Google map
require(ggmap)
map<-get_map(location='Europe', zoom=5, maptype = "terrain",
             source='google',color='color')

# plot it with ggplot2
require("ggplot2")
require("RColorBrewer")
ggmap(map) +
  geom_point(
    aes(x=lon, 
        y=lat, 
        show_guide = TRUE, 
        colour=Number), 
    data=geo, 
    alpha=.8, 
    na.rm = T)  + 
  scale_color_gradient(low="beige", high="blue")

#Set the pointer from (y,x) => (yend,xend) using geom-segment
ggmap(map, extent = "device", ylab = "lat", xlab = "lon") + 
  geom_segment(aes(y = geo$lon, x = geo$lat, yend = geo$lonend, xend = geo$latend))

你对我做错了什么有什么建议吗？

Answer 1

您的线段没有绘制，因为您混淆了纬度和经度，x对应经度，y对应纬度。此外，您应该使用data = geo并从aes()中删除geo$

ggmap(map, extent = "device", ylab = "lat", xlab = "lon") + 
  geom_segment(data = geo, aes(y = lat, x = lon, yend = latend, xend = lonend))

此外，为了显示箭头，只需在geom_segment中添加arrow = arrow()

ggmap(map, extent = "device", ylab = "lat", xlab = "lon") + 
  geom_segment(data = geo, aes(y = lat, x = lon, yend = latend, xend = lonend),
               arrow = arrow())