title: Is it possible to draw a stacked density graph like this one in d3.js?
body: <p>Is it possible to draw a stacked density graph like this one in d3.js?</p>
  
  <p><a href="https://i.stack.imgur.com/l9wse.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l9wse.jpg" alt="NYC 911 calls"></a></p>
  
  <p>Reference: <a href="http://www.wired.com/2010/11/ff_311_new_york/" rel="nofollow noreferrer">http://www.wired.com/2010/11/ff_311_new_york/</a></p>