General-purpose encyclopedia articles, chiefly from Wikipedia, that this atlas cites to support an entity's facts, properties and prose. Belongs here: any source entity representing a Wikipedia or comparable general reference-encyclopedia article, whatever the subject it documents. Does not belong here: an internal cross-reference within this atlas's own system, which belongs under Internal System Reference, or a specialized primary source such as a manufacturer specification sheet or government record, which this atlas does not yet track as a distinct source subcategory.