Map MyMap = MapApplication.Current.Map; LayerCollection MyLayers = MyMap.Layers; Layer BaseLayer = null; foreach (Layer MyLayer in MyLayers) { if ((MyLayer is ArcGISTiledMapServiceLayer) || (MyLayer is OpenStreetMapLayer)) { BaseLayer = MyLayer; } } if (!BaseLayer.Visible) { BaseLayer.Visible = true; } else { BaseLayer.Visible = false; }