docs: function getHeatmap(tracks) {
      var heatmap = [];
      _.each(tracks, function(track) {
          var idxStart = Math.floor(track.startTime / HEATMAP_SEGMENT), idxEnd = Math.ceil(track.endTime / HEATMAP_SEGMENT);
          idxEnd = Math.min(MAX_HEATMAP_LEN, idxEnd); /* Protection - sometimes we have buggy tracks which end in Infinity */
  
          for (var i=idxStart; i<idxEnd; i++) {
            if (i<0) continue;
            if (! heatmap[i]) heatmap[i] = 0;
            USE_BOOLEAN ? heatmap[i] = 1 : heatmap[i]++;
          }
      });
  
      /* Heatmap: Fill in the blanks */
      for (var i = 0; i!=heatmap.length; i++) 
        if (! heatmap[i]) heatmap[i] = 0;   
  
      return heatmap;
  }