//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)");