title: Adding hexbin plots together
body: <p>I have four hexbin plots which have all been normalized. How do I add them together to make one big distribution?
  <img src="https://i.stack.imgur.com/vohKr.png" alt="enter image description here">
  I have tried concatenating the input vectors and then creating the hexbin plot, but this throws off the normalization of the individual distributions:
  <img src="https://i.stack.imgur.com/klWXn.png" alt="enter image description here">
  So how do I add the individual hexbin distributions whilst still maintainging the induvidual normalization?</p>
  
  <p>The relevant part of my code is:</p>
  
  <pre><code>def hex_plot(x,y,max_v):
    bounds = [0,max_v*m.exp(-(3**2)/2),max_v*m.exp(-2),max_v*m.exp(-0.5),max_v]   # The sigma bounds
    norm = mpl.colors.BoundaryNorm(bounds, ncolors=4)
    hex_ = plt.hexbin(x, y, C=None, gridsize=gridsize,reduce_C_function=np.mean,cmap=cmap,mincnt=1,norm=norm)
    print "Hex plot max: ",hex_.norm.vmax
    return hex_
  
  gridsize=50
  cmap = mpl.colors.ListedColormap(['grey','#6A92D4','#1049A9','#052C6E'])
  
  hex_plot(x_tot,y_tot,34840)
  </code></pre>
  
  <p>Thank you.</p>