title: Cartopy set_extent is not working
body: <p>I am trying to use Mateplotlib cartopy to make the plots below. Here is the code that I am using. </p>
  
  <pre><code>import cartopy.crs as ccrs
  
  fig=plt.figure(figsize=(15,11))
  ax = plt.subplot(111, projection=ccrs.PlateCarree(central_longitude=0))
  mm =   ax.contourf(new_lon[:],lat_post,new_aa[0,:,:],transform=ccrs.PlateCarree(central_longitude=0))
  
  ax.coastlines(resolution='10m');
  ax.stock_img();
  # the following two lines increaes the vertical distance between the title and the upper tick.
  from matplotlib import rcParams
  rcParams['axes.titlepad']=20
  # drawing the longitude and latitude ticks.
  gl = ax.gridlines(crs=ccrs.PlateCarree(central_longitude=0), draw_labels=True,linewidth=2, color='gray', alpha=0.5, linestyle='--')
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/ytSKe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ytSKe.png" alt="enter image description here"></a>
  Yet, once I add the following code set_extent
  <code>ax.set_extent([np.min(new_lon),np.max(new_lon),np.min(lat_post)
  ,np.max(lat_post)])</code></p>
  
  <p>The figures becomes like that 
  <a href="https://i.stack.imgur.com/SHr11.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SHr11.png" alt="enter image description here"></a></p>