When Garmin introduced BaseCamp it was only for maps with DEM layers. Now you can view almost all maps except marine charts. The best feature is that you can view IMG-maps (like gmapsupp.img) directly with BaseCamp. It works if the maps resides on a attached Garmin GPS unit in storage mode or with maps on USB memory readers. Files created with MapSource needs modification to set MS flag = 0 which can be done by [Only registered and activated users can see links. ].
I prefer to use MapSource with genuine MapSource maps and possibly BaseCamp to read IMG maps or MapSource maps with DEM layers in 3D simulation.
Use [Only registered and activated users can see links. ] for marine charts like BlueChart g2 Vision.
About "unauthorized" maps