MapPoint point = MapPointBuilderEx.CreateMapPoint(10, 20);
List<Coordinate2D> coords = new List<Coordinate2D>() { new Coordinate2D(50, 60), new Coordinate2D(-120, -70), new Coordinate2D(40, 60) };
Multipoint multipoint = MultipointBuilderEx.CreateMultipoint(coords, SpatialReferences.WebMercator);
Polyline polyline = PolylineBuilderEx.CreatePolyline(coords);
string json = "{\"rings\":[[[0,0],[0,1],[1,1],[1,0],[0,0]],[[3,0],[3,1],[4,1],[4,0],[3,0]]]}";
Polygon polygon = PolygonBuilderEx.FromJson(json);
var geometries = new List<Geometry>() { point, multipoint, polyline, polygon };
//At 2.x - using (var builder = new GeometryBagBuilder(SpatialReferences.WGS84))
var builder = new GeometryBagBuilderEx(SpatialReferences.WGS84);
builder.AddGeometries(geometries);
GeometryBag geomBag = builder.ToGeometry();
// geomBag.PartCount == 4 (point, multipoint, polyline, polygon)
geometries = new List<Geometry>() { point, polyline };
builder.InsertGeometries(1, geometries);
// builder.GeometryCount == 6
geomBag = builder.ToGeometry();
// geomBag.PartCount == 6 (point, point, polyline, multipoint, polyline, polygon)