 			// clean up everything that does not get cleaned up automatically.
 			disposeObjects(
 				backgroundBitmap.bitmapData,
-				plotBitmap.bitmapData,
-				aggregateBitmap.bitmapData
+				plotBitmap.bitmapData
 			);
 			if (!usingExternalSpatialIndex)
 				disposeObjects(spatialIndex);

		 */
		private function init():void
		{
			constantZeroPoint.x = 0;
			constantZeroPoint.y = 0;
			
			// generate a name for debugging
			name = NameUtil.createUniqueName(this);
			// default size = 100%,100%
			percentWidth = 100;
			percentHeight = 100;
			
			//this.addChild(backgroundBitmap);
			//this.addChild(plotBitmap);
			this.addChild(aggregateBitmap);
			
			// make selectionFilter appear in session state.
			registerLinkableChild(this, selectionFilter);

				if (shouldDraw)
				{
					var keys:Array = getSelectedKeys() || []; // use empty Array if keys are null
					plotter.drawPlot(keys, _dataBounds, _screenBounds, plotBitmap.bitmapData);
				}
			}
		}
		
		/**
