From World Wind Wiki
A RenderableObject is anything that World Wind can draw on the globe. They can be created either programatically at any time in a plugin, or at startup from xml configuration files. The xml files allow you to add simple objects to the globe without having to write any code, while a plugin lets you extend existing objects or create new ones in ways that are impossible using the xml config files.
World Wind's available RenderableObjects and the xml tags necessary to create them are described below. For specific examples, see any number of existing World Wind add-ons.
 Creating RenderableObjects from plugins
See detailed documentation here.
 Creating RenderableObjects from config files
The root element in a World Wind config file is the LayerSet. Each xml file must have exactly one set of LayerSet tags. All of the objects described below will be inside the LayerSet element.
A LayerSet corresponds to a root-level item in the World Wind layer manager. If an xml file contains a LayerSet with the same name as one that already exists then the items in the xml file will be added to the existing layer in World Wind. Options for a LayerSet are controlled using attributes for the LayerSet element.
 LayerSet attributes
 Name (required, string)
The name of the LayerSet.
 RenderableObject attributes
These attributes apply to all RenderableObjects, including LayerSet.
 ShowAtStartup (optional, boolean)
Controls whether the item is checked at startup. Default value is "false".
 InfoUri (optional, string)
A web address. Including this attribute will make the name of the object in the layer manager a clickable link.