A distinct set of geographic features of the same type displayed together in a GIS, such as roads, parcels, buildings, or water bodies.
GIS maps are built by stacking layers. Each layer contains one type of geographic feature — all the roads in one layer, all the buildings in another, all the water bodies in a third. Layers can be turned on or off, styled independently, and analyzed in combination with other layers.
Example: A municipal GIS has separate layers for: property parcels, building footprints, road centrelines, water mains, sewer lines, and zoning boundaries. An urban planner can display only the layers relevant to a specific analysis — for example, parcels and zoning — without the visual clutter of unrelated layers.
The concept of layers is fundamental to how GIS organizes and presents geographic data. Most GIS file formats, including shapefiles and GeoJSON, store one layer per file.