title: Wrap legend text in ggplot2
body: <p>Whilst producing graphs using ggplot2, I have some long legend names which I wish to wrap over two lines. For example:</p>
  
  <pre><code>a &lt;- (1:10)
  b &lt;- c(1,1.5,2,4,5,5.3,7,9,9.5,9.8)
  places = c("Birmingham","Chester-le-street","Cambridge", "Newcastle-upon-Tyne","Peterborough","Cambridge", "Newcastle-upon-Tyne","Peterborough","Liverpool","Stratford-upon-Avon")
  df1 = data.frame(a,b,places)
  library(ggplot2)
  i = ggplot(df1, aes(x=a, y=b)) + geom_point(aes(colour = places), size=3) + opts(legend.position="bottom")
  </code></pre>
  
  <p>How would I go about wrapping the legend items when the box is set to be at the bottom - say in 2 or 3 lines?  At the moment the seven items of the legend are next to each other.  I would prefer that they are displayed in two rows (with say four towns on the top row and three towns on the second row).</p>
  
  <p>Many thanks in advance.</p>