private void updatePointToolStripMenuItem_Click(object sender, EventArgs e)
{
IMultipoint multipoint;
object missing = Type.Missing;
IPoint point1 = new PointClass();
point1.PutCoords(10, 10);
IPoint point2 = new PointClass();
point2.PutCoords(20, 20);
IPointCollection pointCollection = new MultipointClass();
pointCollection.AddPoint(point1, ref missing, ref missing);
pointCollection.AddPoint(point2, ref missing, ref missing);
point1 = new PointClass();
point1.PutCoords(40, 10);
pointCollection.UpdatePoint(1, point1);
multipoint = pointCollection as IMultipoint;
addFeature("multipoint", multipoint as IGeometry);
System.Windows.Forms.MessageBox.Show("X = " + pointCollection.get_Point(1).X +
", Y = " + pointCollection.get_Point(1).Y);
this.axMapControl1.Extent = multipoint.Envelope;
this.axMapControl1.Refresh();
}