Gets or sets the image map associated with the chart.
The image map defines "hot spots" on the chart that may have tool tips, becomes clickable and responses to other mouse events.
WebChartViewer expects the image map to be in HTML image map format comprising of <AREA> tags only. No <MAP> tag should be included in the image map as WebChartViewer will generate the <MAP> tag automatically.
The image map for a chart can be generated automatically by using BaseChart.getHTMLImageMap.