title: choropleth in ggmap not plotting correctly
body: <p>I think I just made the world's weirdest choropleth.  </p>
  
  <p>The code is simple:  </p>
  
  <pre><code>df$cut &lt;- cut_interval(df$Count, 5)
  
  ggplot(df, aes(lon, lat)) +
    geom_polygon(aes(fill = df$cut), colour = alpha("white", 1/2), size = 0.2) + 
    geom_polygon(data = df , colour = "white", fill = NA) +
    scale_fill_brewer(palette = "PuRd")
  </code></pre>
  
  <p>(see <a href="http://pastebin.com/30SHHqGu" rel="nofollow noreferrer">Pastebin</a> for a <code>dput</code> of the dataframe)  </p>
  
  <p>But the map is crazy:  </p>
  
  <p><a href="https://i.stack.imgur.com/HL6E9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HL6E9.png" alt="enter image description here"></a></p>
  
  <p>Where did I go wrong?  </p>
  
  <p>Looking at other <a href="https://gist.github.com/hadley/233134" rel="nofollow noreferrer">code</a> snippets, I can't seem to figure out how to make this work.</p>