title: geom_polygon in ggplot2 - Facets for different fillings?
body: <p>is there a way of combining these three maps using facets?</p>
  
  <pre><code>emi &lt;- readShapePoly('prov2011_g.shp')
  names(emi) &lt;- c('REG', 'ID', 'NOME', 'SHAPE', 'AREA', 'MIG1', 'MIG2', 'MIG3')
  emi_geom &lt;- poly_coords(emi)
  
  map &lt;- qplot(PolyCoordsY, PolyCoordsX, data = emi_geom, group = Poly_Name, geom = 'polygon', fill = MIG1)
  
  map1 &lt;- qplot(PolyCoordsY, PolyCoordsX, data = emi_geom, group = Poly_Name, geom = 'polygon', fill = MIG2)
  
  map2 &lt;- qplot(PolyCoordsY, PolyCoordsX, data = emi_geom, group = Poly_Name, geom = 'polygon', fill = MIG3)
  </code></pre>
  
  <p>I followed this great tutorial (<a href="http://www.r-bloggers.com/maps-with-ggplot2/" rel="nofollow">http://www.r-bloggers.com/maps-with-ggplot2/</a>). The poly_coords function exctracts coordinates out of a shapefile. I have tried to use melt (reshape2) but I don't know how to apply it to this case - with other geom_* is a lot easier.
  Hope you can help me out.</p>