Every GIS System consists of Layers.
The advantage of GIS Systems over paper maps is that you can decide what information you want to view on the map at any given time. Of the dozen or so layers loaded into the Project, the User can only view one, because only one interests them. This makes the map elegant and provides for quick visual analysis.
Deciding which layers you want to view is what Activate and Deactivate Layers are all about.
