title: ggmap visualization of data with circles on map
body: <p>I am trying to create a map that shows in circles the cities where subjects in my data set originated. I would like the circles to be proportional to the number of people in the city in my data. I would also like an additional circle to be a subset of the original circle showing the people in each city afflicted by the disease.</p>
  
  <p>I have started doing this with ggmap by getting longitudes and latitudes:</p>
  
  <pre><code>library(ggplot2) 
  library(maps)
  library(ggmap)
  geocode("True Blue, Grenada")
  </code></pre>
  
  <p>I'm stuck because I don't know how to continue. I can't load the US map alone because there is one location in the Caribbean.</p>
  
  <p>here is my data in short format, the actual data set is far too large.</p>
  
  <pre><code>subjectid   location            disease
  12          Atlanta, GA         yes
  15          Boston, MA          no
  13          True Blue, Grenada  yes
  85          True Blue, Grenada  yes
  46          Atlanta, GA         yes
  569         Boston, MA          yes
  825         True Blue, Grenada  yes
  685         Atlanta, GA         no
  54          True Blue, Grenada  no
  214         Atlanta, GA         no
  685         Boston, MA          no
  125         True Blue, Grenada  yes
  569         Boston, MA          no
  </code></pre>
  
  <p>can someone please help?</p>