Sources

The bibliography the atlas's entities cite: encyclopedia entries, academic journals, professional and institutional pages and the rest of the source types the atlas cites, each one a real page a reader could open and check for themselves. This category exists so a citation itself is addressable and browsable in its own right, not because a source is a subject of study, and it lets a reader see the full range of material an atlas has drawn on rather than only the citation attached to one fact.