The top-level groupings this atlas organizes its content types into: Crafts, Hobbies and Pastimes, Tools and Equipment, Figures, Institutions and Societies, Concepts and Movements, Milestones and Projects and Patterns, plus the structural reference types Sources, Open Questions, Relation Types, Sections and Subcategories beneath them. Each category is itself an entity so a reader can browse straight to it, and each carries the same kind of description this entry does, saying what belongs and what deliberately does not.