What is a graphics layer
Graphics layers allow you to display graphics on a map. Graphics can have point, polyline, and polygon geometries. A graphics layer can, for example, be used to hold polygons drawn by a user or display features that satisfy a user-defined query or showing a real-time Global Positioning System (GPS) location. Graphics in a graphics layer are stored in memory and are only available while the application is running. Graphics layers are therefore very well suited to displaying large numbers of symbols which are updated in a real time environment.
When a feature is drawn in the graphics layer, it will have a number of properties set that will define its appearance. The feature's geometry and attributes, combined with symbol properties, is known as a graphic. Graphics are assigned to a graphics layer where they are rendered.