protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                InMemoryMarkerOverlay inmemoryFeatureLayer = new InMemoryMarkerOverlay();
                inmemoryFeatureLayer.Columns.Add(new FeatureSourceColumn("imageType"));

                MarkerValueItem item1 = new MarkerValueItem("image1", new PointMarkerStyle(new WebImage("../../theme/default/samplepic/city.png")));
                MarkerValueItem item2 = new MarkerValueItem("image2", new PointMarkerStyle(new WebImage("../../theme/default/samplepic/circle.png")));

                Collection<MarkerValueItem> items = new Collection<MarkerValueItem>();
                items.Add(item1);
                items.Add(item2);

                ValueMarkerStyle valueStyle = new ValueMarkerStyle("imageType", items);
                inmemoryFeatureLayer.ZoomLevelSet.ZoomLevel01.CustomMarkerStyle = valueStyle;
                inmemoryFeatureLayer.ZoomLevelSet.ZoomLevel01.ApplyUntilZoomLevel = ApplyUntilZoomLevel.Level20;

                Feature feature1 = new Feature(0, 0);
                feature1.ColumnValues["imageType"] = "image1";
                Feature feature2 = new Feature(0, 10);
                feature2.ColumnValues["imageType"] = "image2";

                inmemoryFeatureLayer.Features.Add(feature1);
                inmemoryFeatureLayer.Features.Add(feature2);

                Map1.CurrentExtent = new RectangleShape(-180, 90, 180, -90);
                Map1.MapUnit = GeographyUnit.DecimalDegree;
                Map1.CustomOverlays.Add(inmemoryFeatureLayer);
            }
        }