title: R-Map with color points depending on the category
body: <p>I need to create a map with point given by coordinates <strong>but with different colors depending on a variable (let's say 'cat').</strong></p>
  
  <pre><code>data1=data.frame(X=c(-122,-122,-122), Y=c(37,37,38), cat=c('A', 'A', 'B'))
      map &lt;- qmap('San Francisco', zoom = 12, maptype = 'hybrid')
      map + geom_point(data = data1, aes(x = X, y = Y), color="red", size=1, alpha=0.5)
  </code></pre>
  
  <p>I though to introduce color=cat but didn't work.</p>