title: Matplotlib - how to superimpose a contour map with coastlines and countries
body: <p>I have this python script that plots a contour map of geopotential heights - </p>
  
  <pre><code>nc_f = './hgt_500_2014_12_5_00Z.nc'  # Your filename
  nc_fid = Dataset(nc_f, 'r')
  
  lats = nc_fid.variables['lat'][:]  # extract/copy the data
  
  lons = nc_fid.variables['lon'][:]
  
  time = nc_fid.variables['time'][:]
  hgt = nc_fid.variables['hgt'][:]  # shape is time, lat, lon as shown above
  
  x, y = np.meshgrid(lons, lats,copy=False)
  
  rbf = scipy.interpolate.Rbf(x, y, hgt, function='linear')
  zi = rbf(x, y)
  plt.contour(x,y,zi)
  plt.show()
  </code></pre>
  
  <p>I want to be able to superimpose this plot with coastlines and countries.
  I tried this but this gives me  the coastlines and countries but the geopotential height contours are missing</p>
  
  <pre><code> m = Basemap(width=5000000,height=3500000,
          resolution='l',projection='stere',\
          lat_ts=40,lat_0=lat_0,lon_0=lon_0)
  
  
   x, y = np.meshgrid(lons, lats,copy=False)
  
   rbf = scipy.interpolate.Rbf(x, y, hgt, function='linear')
   zi = rbf(x, y)
  
   cs = m.pcolor(x,y,np.squeeze(hgt))
  
  
  
   m.drawcoastlines()
   m.drawcountries()
   cs = m.contour(x,y,zi,15,linewidths=1.5)
  
  cbar = m.colorbar(cs, location='bottom', pad="10%")
  cbar.set_label(hgt_units)
  
  plt.title('500 hPa Geopotential Height')
  plt.savefig('testplot.png')
  plt.show() 
  </code></pre>