title: Big dataset contour plot using pyplot and pandas
body: <p>I have a massive data sample and need to visualize it. Using pandas, I can create a dataframe with relevant variables- 3 arrays of length 20Million.</p>
  
  <p>These are x,y geometrical coordinates and z value on that (x,y) point. </p>
  
  <p>I need a "heatmap" of z at each (x,y) point. But no pyplot function works with numbers this big.</p>
  
  <p>What is the best way to go about it?</p>