GIS Concept # 2: Information is separated into layers.
We can also have other layers of information in our GIS. Our information on trees would constitute one layer of information. We could also have a layer with rivers and a layer with soil types. Any information can be represented as a layer.
A map represents the landscape in an artificial way. Vector layers represent features in one of several ways:
A point is good for representing information in which it is necessary to show where a feature is, but its physical shape is not important (i.e. trees in the old growth tree layer).
A line is suitable to represent many real world features (i.e. the rivers in the river layer).
Don't be intimidated by the name. It is really just a solid multi-sided shape. When you see a polygon, remember that everything inside the boundary has the attributes associated with the record. (i.e. soil types in the soils layer)
You might hear people talk about coverages, themes, or shapefiles. All these terms are other names for layers of information.
With individual layers we can conduct analysis between layers and only display layers of interest.
As you work with BGIS maps you will be able to turn different layers on and off as you desire.