title: Library to generate heat map map overlay based off point values not point densities
body: <p>I have a set of data points where each point is expressed as a lat/lng.  Each of these points has a value associated with it that changes over time.  I would like to produce a heatmap animation overlay on top of a map that reflects this change in value over time.  Note: I am fine with producing a series of static "snapshots" and piecing them together frame-by-frame into an animation, so the heatmap library itself does not have to support animation.  </p>
  
  <p>My first attempt was to use the <a href="https://developers.google.com/maps/documentation/javascript/reference#HeatmapLayer" rel="nofollow noreferrer">HeatMapLayer</a> which is a part of the Google Maps visualization library. However as per the question <a href="https://stackoverflow.com/q/14461954/129475"><em>Heatmap based on average weights and not on the number of data points</em></a>, it would seem that this particular visualization library insists on weighing the <em>density</em> of points in determining what color to use surrounding a given point.  </p>
  
  <p>I am after a solution that only considers the value of the points rather than the density.  To give an example, assume one wanted to visualize the ambient temperature of a city over time, but there were more thermometers installed in some parts of the city than others.  You wouldn't want a small area with many thermometers installed to show up red just because there were many thermometers - you'd want it to show up red only if it was hot there.</p>
  
  <p>Basically, I want a single color for each of my points that reflects the intensity of the point's value, and then a gradient spatial transition between any two point's colors.  It doesn't have to be Google Maps - the key criteria is just <code>i)</code> must base colors off point values not point densities <code>ii)</code> must overlay on top of a map and <code>iii)</code> ideally has a programming abstraction that talks in terms of lat/lng's, rather than requiring manual conversion to e.g. Euclidean space.  </p>