Defines the graphic's appearance when displayed in a map view or scene view. For graphics to appear in a map view or scene view, they must have a Symbol or be added to a graphics overlay that has a renderer assigned. A Symbol defines the properties used to display the graphic, such as color, outline, size, and style. There are many different types of symbols, such as SimpleMarkerSymbol, SimpleLineSymbol, and SimpleFillSymbol. The symbol type must match the GeometryType of the graphic. For example, a FillSymbol is used with graphics that are based on polygon geometry. The rendering of a graphic's symbol takes precedence over the Renderer that may be set on the GraphicsOverlay.