anchor.diff:      // {'point': [x, y],
       //  'value': v,
       //  'color': c,
  +    //  'uri': path,
       //  ...
       // }
       assert(dataPoint.containsKey('point'));
  
positive.code: 
    // Record maximum values of x and y which represent the width and height for
    // background necessary for zooming and panning.
    num maxX, maxY;
    maxX = maxY = double.NEGATIVE_INFINITY;
  
    for (Map dataPoint in data) {
  
negative.code:     } else {
        color = dataPoint['color'];
      }
  
      // Create the circle element
      svg.CircleElement point = new svg.CircleElement();
      point.attributes = {
        'cx': '${dataPoint['point'][0] - minX.toInt()}',
        'cy': '${dataPoint['point'][1] - minY.toInt()}',
        'r': '2',
        'fill': color,
      };
  