public void AddPolygon(PointF[] polygon, string[] entries, Color fill)
        {
            MapPolygon mp = new MapPolygon(polygon);
            mp.Fill = fill;

            AddMapObject(mp);

            if (entries == null)
                return;

            // add the MapPolygon to the entries
            foreach (string key in entries)
            {
                List<MapPolygon> pl;
                if (!_DataPoints.TryGetValue(key, out pl))
                {
                    pl = new List<MapPolygon>();
                    _DataPoints.Add(key, pl);
                }
                pl.Add(mp);
            }
        }