title: Density map (heatmaps) in matplotlib
body: <p>I have a list of coordinates:</p>
  
  <pre><code>y,x
  445.92,483.156
  78.273,321.512
  417.311,204.304
  62.047,235.216
  87.24,532.1
  150.863,378.184
  79.981,474.14
  258.894,87.74
  56.496,222.336
  85.105,454.176
  80.408,411.672
  90.656,433.568
  378.027,441.296
  433.964,290.6
  453.606,317.648
  383.578,115.432
  128.232,312.496
  116.276,93.536
  94.072,222.336
  52.226,327.308
  321.663,187.56
  392.972,279.008
  </code></pre>
  
  <p>I would like to plot a density map (or heat map) based on these points, using matplotlib. I am using pcolormesh and contourf. 
  My problem is that pcolormesh is not having same size of the pitch: 
  <a href="https://i.stack.imgur.com/ZKkK7.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ZKkK7.png" alt="enter image description here"></a></p>
  
  <p>This is the code:</p>
  
  <pre><code>x, y = np.genfromtxt('pogba_t1314.csv', delimiter=',', unpack=True)
  
  #print(x[1], y[1])
  y = y[np.logical_not(np.isnan(y))]
  x = x[np.logical_not(np.isnan(x))]
  k = gaussian_kde(np.vstack([x, y]))
  xi, yi = np.mgrid[x.min():x.max():x.size**0.5*1j,y.min():y.max():y.size**0.5*1j]
  zi = k(np.vstack([xi.flatten(), yi.flatten()]))
  
  fig = plt.figure(figsize=(9,10))
  ax1 = fig.add_subplot(211)
  
  
  ax1.pcolormesh(xi, yi, zi.reshape(xi.shape), alpha=0.5)
  
  ax1.plot(y,x, "o")
  ax1.set_xlim(0, 740)
  ax1.set_ylim(515, 0)
  
  #overlay soccer field
  im = plt.imread('statszone_football_pitch.png')
  ax1.imshow(im, extent=[0, 740, 0, 515], aspect='auto')
  
  
  fig.savefig('pogba1516.png')
  </code></pre>
  
  <p>Here it is a link for the csv file: <a href="https://dl.dropboxusercontent.com/u/12348226/pogba_t1314.csv" rel="noreferrer">https://dl.dropboxusercontent.com/u/12348226/pogba_t1314.csv</a></p>