title: How do I plot US cities using ggplot?
body: <p>I can plot the state of Louisiana just fine...</p>
  
  <pre><code>require(ggplot2)
  require(ggmap)
  require(maps)
  LA &lt;- map_data("state", region="louisiana")
  ggplot(LA, aes(x=long, y=lat))+geom_polygon()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/dNfb8.png" alt="enter image description here">    </p>
  
  <p>Now, I have data on how many sales calls were made to particular cities in LA.  How would I add a point for each city where a sales call was made to the plot?</p>
  
  <pre><code>salesCalls &lt;- data.frame(State=rep("louisiana",5), 
                               City=c("Baton Rouge", "New Orleans", "Shreveport", "Lafayette", "Mandeville"),
                               Calls=c(10,5,8,13,2))
  salesCalls
        State        City Calls
  1 louisiana Baton Rouge    10
  2 louisiana New Orleans     5
  3 louisiana  Shreveport     8
  4 louisiana   Lafayette    13
  5 louisiana  Mandeville     2
  </code></pre>