docs: function (zMin, zMax, minSize, maxSize) {
  		var len,
  			i,
  			pos,
  			zData = this.zData,
  			radii = [],
  			sizeByArea = this.options.sizeBy !== 'width',
  			zRange;
  		
  		// Set the shape type and arguments to be picked up in drawPoints
  		for (i = 0, len = zData.length; i < len; i++) {
  			zRange = zMax - zMin;
  			pos = zRange > 0 ? // relative size, a number between 0 and 1
  				(zData[i] - zMin) / (zMax - zMin) : 
  				0.5;
  			if (sizeByArea && pos >= 0) {
  				pos = Math.sqrt(pos);
  			}
  			radii.push(math.ceil(minSize + pos * (maxSize - minSize)) / 2);
  		}
  		this.radii = radii;
  	}