title: How to plot the grid line only using pcolor/pcolormesh
body: <p>By using <code>ax.axhline</code> &amp; <code>ax.axvline</code> I can plot the grid network shows like this:</p>
  
  <p><a href="http://i4.tietuku.com/e90652c9a56b5e61.png" rel="nofollow noreferrer">http://i4.tietuku.com/e90652c9a56b5e61.png</a></p>
  
  <p>the code are reproduced here:</p>
  
  <pre><code> lon_grid  = np.linspace(113.5,115.49,36)
   lat_grid  = np.linspace(37.40,38.78,30)
  
   lon_grid,lat_grid = np.linspace(xc1,xc2,36), np.linspace(yc1,yc2,30)
   for i in range(0,len(lon_grid),1):
       ax.axvline(x=lon_grid[i], linestyle='-', color='black', linewidth=0.75,    zorder=3)
   for i in range(0,len(lat_grid),1):
       ax.axhline(y=lat_grid[i], linestyle='-', color='black', linewidth=0.75, zorder=3)         
  </code></pre>
  
  <h3>Here is my question</h3>
  
  <p>Can I use pcolor/pcolrmesh to just draw the outline of the grid </p>