3.3.1 The layers
GIS uses the notion of layers to process geographic data sets. A layer is a set of geographic objects of the same type (e.g. a layer of roads, a layer of water points) that can come from different sources on which we can perform analyses or apply representations using symbols and labels.
Layers in a GIS
Each map is the result of a compilation of different layers displayed on top of each other in a specific order.