InMemoryFeatureLayer inmemoryFeatureLayer = new InMemoryFeatureLayer();
            inmemoryFeatureLayer.ZoomLevelSet.ZoomLevel01.DefaultPointStyle.PointType = PointType.Bitmap;
            inmemoryFeatureLayer.ZoomLevelSet.ZoomLevel01.DefaultPointStyle = new PointStyle(new GeoImage(@".......\marker.png"));
            inmemoryFeatureLayer.ZoomLevelSet.ZoomLevel01.ApplyUntilZoomLevel = ApplyUntilZoomLevel.Level20;
            Random ra = new Random();
            for (int i = 0; i < 20000; i++)
            {
                int x = ra.Next(0, 1800);
                int y = ra.Next(0, 900);
                double dx = x / 10;
                double dy = y / 10;
                PointShape point = new PointShape(dx, dy);
                Feature fe = new Feature(dx, dy);
                inmemoryFeatureLayer.InternalFeatures.Add(fe);
            }
            inmemoryFeatureLayer.BuildIndex();
            LayerOverlay overLay = new LayerOverlay();
            overLay.TileCache = new FileBitmapTileCache(@"c:\temp2");
            overLay.TileCache.CacheId = "cache";
            overLay.Layers.Add(inmemoryFeatureLayer);

            inmemoryFeatureLayer.Open();
            wpfMap.CurrentExtent = inmemoryFeatureLayer.GetBoundingBox();
            inmemoryFeatureLayer.Close();

            wpfMap.Overlays.Add(overLay);
            wpfMap.Refresh();