public void Handle_MouseDown(object sender, MouseEventArgs args)
{
slider.Fill = new SolidColorBrush(Colors.Green);
Rectangle item = sender as Rectangle;
mouseHorizontalPosition = args.GetPosition(null).X;
BelowMap.Extent = AboveMap.Extent;
BelowMap.Visibility = Visibility.Visible;
isMouseCaptured = true;
item.CaptureMouse();
}