title: SpatialPolygonDataFrame plotting using ggplot
body: <p>I have a shape file for the greater London area. I use the <code>readShapePoly</code> function from the <code>maptools</code> package to load it in R as a <code>SpatialPolygonDataFrame</code> .</p>
  <p>I want to the plot those polygons .. Which I have already done by using the basic of <code>plot</code> function in R.
  The output looks as shown in this image:</p>
  <p><img src="https://i.stack.imgur.com/soh9k.png" alt="plot of London" /></p>
  <p>Now, I am trying to plot the same shape file using <code>ggplot2</code> but it doesn't work for me.
  I am getting some weird lines in the graph as shown below:
  <img src="https://i.stack.imgur.com/dRgRr.png" alt="ggplot2 of London" /></p>
  <p>The code I used was :</p>
  <pre><code>london.wards &lt;- readShapePoly(&quot;~/TD/london_wards2013/london_wards2013.shp&quot;
                            , proj4string=CRS(projString))
  wards.count &lt;- nrow(london.wards@data)
  # assign id for each lsoa
  
  london.wards@data$id &lt;- 1:wards.count
  wards.fort &lt;- fortify(london.wards, region='id')
  ggplot(wards.fort, aes(long, lat)) + geom_polygon(colour='black', fill='white')
  </code></pre>
  <p>where projString is the projection string describing the projection used for the input shape file.</p>