public IReadOnlyList<Layer> GetLayersAsFlattenedList()

List<FeatureLayer> featureLayerList = aMap.GetLayersAsFlattenedList().OfType<FeatureLayer>().ToList();

//Get an existing Layer. This layer has a symbol you want to use in a new layer.
var lyr = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>()
      .Where(l => l.ShapeType == esriGeometryType.esriGeometryPoint).FirstOrDefault();

//Finds layers by name and returns a read only list of Layers
IReadOnlyList<Layer> layers = aMap.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)");

Map map = MapView.Active.Map;
IEnumerable<Layer> matches = map.GetLayersAsFlattenedList().Where(l => l.Name.IndexOf(partialName, StringComparison.CurrentCultureIgnoreCase) >= 0);