private void Button_ClearMap(object sender, RoutedEventArgs e)
{
List<GraphicsLayer> graphicsLayers = new List<GraphicsLayer>();
foreach (Layer layer in MyMap.Layers)
if (layer is GraphicsLayer)
graphicsLayers.Add(layer as GraphicsLayer);
for (int i = 0; i < graphicsLayers.Count; i++)
MyMap.Layers.Remove(graphicsLayers[i]);
}