title: Present different colors in contourf
body: <p>I want to present a 2D matrix, like in below for example:</p>
  
  <pre><code>2 3 4 5 6 3
  1 2 2 4 5 5
  1 2 2 2 2 4
  </code></pre>
  
  <p>I use <code>contourf</code> in <code>matplotlib</code>,to do the work,</p>
  
  <pre><code>cmap = colors.ListedColormap(['0.75', (0.2, 0.3, 0.5), 'r', 'b', 'g', 'c'])
  bounds = [-0.5, 0.5, 1.5, 2.5, 3.5, 4.5]
  norm = colors.BoundaryNorm(bounds, cmap.N)
  
  map = plt.contourf(x, y, Cordi, cmap=cmap, norm=norm, 
                     level=[1,2,3,4,5], vmin=1, vmax=6)
  </code></pre>
  
  <p>Now here is the problem, there are so many ways to set the colors, I want to know which is in charge of what and who has the priority.</p>
  
  <ol>
  <li><p>In my colormap, there is a <code>bounds</code> which limits the color in a special range</p></li>
  <li><p>In contourf, there is a <code>level</code> which controls the same thing</p></li>
  <li><p>In controuf, there is a <code>vmin</code> and <code>vmax</code> which also controls the same thing</p></li>
  </ol>
  
  <p>I know <code>imshow</code> is more proper for my case and it has already worked successfully. But now when it comes to <code>contourf</code>, there is a <code>level</code> inside, which just makes me confused.</p>
  
  <p>Thank you for viewing my question.</p>