title: Google Maps 'heatmap' that can handle density AND data values?
body: <p>I have locations that have quality 'X', where X can be a negative or positive value. I would like to plot negative values of X as red, and positive values as green. Intermediate values will be yellow. The opacity of the color will correspond to local density of data.</p>
  
  <p><a href="http://code.google.com/p/fusion-tables/issues/detail?id=85" rel="nofollow">Issue 85</a> proves that fusion tables alone can't do this yet. Is there a viable extension that can handle this style of heatmapping?</p>
  
  <p>I've made a mockup of what I want <a href="http://i.imgur.com/gDaba.jpg" rel="nofollow">here</a>.</p>
  
  <p>I don't know if variable transparency will be an inherent problem. Would that even be possible for a Google Map overlay?</p>