title: How to plot arrows on map in R with ggmap
body: <p>I am trying to make a geographical plot in R with points of various airports, and then arrows between them, indicating a particular flight route. </p>
  
  <p>According to some earlier questions here on stack overflow, this should be possible using ggmap and geom_segment, but it seems like it wont work using the approach i have in my code below:</p>
  
  <pre><code>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 &lt;- geocode(location = Adress, output="latlon", source="google")
  
  #moving the data around, so that second observation will be end-destination
  geo$lonend[1] &lt;- geo$lon[2]
  geo$latend[1] &lt;- geo$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&lt;-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) =&gt; (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))
  </code></pre>
  
  <p>Do you have any suggestions for what I am doing wrong?</p>