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:

• You can access attribute information for feature layers by opening the layer's attribute table, clicking on a feature using the Identify tool, or utilizing HTML pop-ups.
• You work with map layers to edit data and add new features.
• You can drag and drop layers as inputs into analytic models using geoprocessing, and model results are often viewed and explored as new map layers.
• There are a number of toolbars for working with map layers, depending on the type of layer. For example, you can work with image layers using a special image classification toolbar.