A layer serves as a shortcut to data. It also tells ArcMap how the data should be drawn. You can store layers in a place that is accessible to everyone in your organization who needs a particular set of data; the data will be displayed the same way for each of them. As useful as layers are, sometimes they are not available. Fortunately, you can add raw geographic data to a map just as easily as you can add a layer.

When you add features directly from a coverage, shapefile, or database, they are all drawn with a single symbol.

Geodatabases containing feature datasets and feature classes are how ArcGIS applications manage geographic information.