public Layer FindLayer( 
   string layerURI,
   bool recursive
)

{
    //Finds layers by name and returns a read only list of Layers
    IReadOnlyList<Layer> layers = map.FindLayers("cities", true);

    //Finds a layer using a URI.
    //The Layer URI you pass in helps you search for a specific layer in a map
    var lyrFindLayer = MapView.Active.Map.FindLayer("CIMPATH=map/u_s__states__generalized_.xml");

    //This returns a collection of layers of the "name" specified. You can use any Linq expression to query the collection.  
    var lyrExists = MapView.Active.Map.GetLayersAsFlattenedList()
                       .OfType<FeatureLayer>().Any(f => f.Name == "U.S. States (Generalized)");
}