title: R - how to get a smooth curve between two points?
body: <p>I'm trying to draw a line between two cities, on a world map, using R (using map and wrld_simpl).  </p>
  
  <p>How can I get a smooth line between the two points?  If I drew a line between US and Australia, it has three different segments</p>
  
  <pre><code>require(rworldmap)
  
  map("world", col="#f2f2f2", fill=TRUE, bg="white", lwd=0.05)
  
  data(wrld_simpl)
  
  US_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'United States']
  US_lon = wrld_simpl$LON[wrld_simpl$NAME == 'United States']
  
  australia_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'Australia']
  australia_lon = wrld_simpl$LON[wrld_simpl$NAME == 'Australia']
  
  lines(c(US_lon, US_lat), c(australia_lon, australia_lat))
  </code></pre>
  
  <p>This draws a line, but it isn't correctly between aus and US.  what am I doing wrong?</p>