A region contains a bounding box () that describes an area of interest defined by geographic coordinates and altitudes. In addition, a Region contains an LOD (level of detail) extent () that defines a validity range of the associated Region in terms of projected screen size. A Region is said to be "active" when the bounding box is within the user's view and the LOD requirements are met. Objects associated with a Region are drawn only when the Region is active. When the is onRegion, the Link or Icon is loaded only when the Region is active.