What is a layer?

Layers are the mechanism used to display geographic datasets in ArcMap, ArcGlobe, and ArcScene. Each layer references a dataset and specifies how that dataset is portrayed using symbols and text labels. When you add a layer to a map, you specify its dataset and set its map symbols and labeling properties.

Each map, globe, or scene document in ArcGIS is assembled by adding a series of layers. Layers are displayed in a particular order displayed in the map's table of contents. Layers listed at the bottom are displayed first, followed by the layers above them.

Layers provide one of the primary ways that you work with geographic data in ArcGIS. For example: