The ArcGIS JavaScript, Flex and Silverlight Web APIs offer a feature layer class for working with client-side graphic features. Feature layers are also used in various forms in ArcGIS Desktop, ArcGIS Explorer and other APIs.

In the version 2.0 and above, the FeatureLayer class extends from the GraphicsLayer class, and offers additional capabilities such as the ability to perform queries and selections. Feature layers are also used for web editing. Equivalent classes also exist in the and Web APIs.

Feature layers differ from tiled and dynamic map service layers because feature layers bring geometry information across to the client computer to be drawn by the web browser. Feature layers potentially cut down on round trips to the server. A client can request the features it needs, then perform selections and queries on those features without having to request more information from the server. Feature layers are especially appropriate for layers that respond to user interaction, such as a mouse click or hover.

More information is available on Inside Feature Layers.

Feature layers also exist in other ArcGIS products and APIs:

See also: What's the difference between feature class and feature layer?