title: R cannot find the function get_map
body: <p>I'm trying to make a google map with R, with this <code>r_google_maps.r</code> script: </p>
  
  <pre><code>require(ggmap)
  
  mapImageData1 &lt;- get_map(location = c(lon = -0.016179, lat = 51.538525),
      color = "color",
      source = "google",
      maptype = "satellite",
      zoom = 17)
  
  ggmap(mapImageData1,
      extent = "device",
      ylab = "Latitude",
      xlab = "Longitude")
  </code></pre>
  
  <p>and I call <code>source("r_google_maps.r");</code> in the command window,</p>
  
  <p>I get this error : </p>
  
  <blockquote>
    <p>Error in eval(expr, envir, enclos) : could not find function "get_map"</p>
  </blockquote>
  
  <p>How do I solve this problem?</p>
  
  <p>Thanks !</p>
  
  <h2>Edit:</h2>
  
  <p>I'm on windows 7 64-bit</p>