title: Mark a specific level in contour map on matplotlib
body: <p>Can anyone give me an example of how to mark a specific level in a contour map?
  I would like to mark the level which is the black line in this plot:</p>
  
  <p><img src="https://i.stack.imgur.com/uCbh8.png" alt="Contour map in which I want to mark a level"></p>
  
  <p>I am using the following code:</p>
  
  <pre><code>plt.figure()
  
  CS = plt.contour(X, Y,log_mu,levels = [np.log10(5e-8),np.log10(9e-5)])
  CS = plt.contourf(X, Y,log_mu)
  CB = plt.colorbar(CS, shrink=0.8, extend='both')
  
  plt.xscale('log')
  plt.yscale('log')
  
  plt.show()
  </code></pre>
  
  <p>And the data for this specific plot can be obtained here <a href="http://dpaste.com/0J3VJST" rel="noreferrer">dpaste data for contour plot</a></p>