val baseLayers: MutableList<Layer>
The collection of base layers in this basemap. Base layers are drawn beneath all other layers in the ArcGISMap or ArcGISScene. They are designed to provide a visual reference to help orient the user. Aerial imagery, terrain, and streets are examples of basemap layers. The collection can be empty but it is never null.
This collection is specific to this basemap so you cannot reuse a collection coming from another Basemap.
List Impl. Mutable List Impl