A map of subjects and unanswered requests.

Coverage follows complete imported source snapshots, not a claim to enumerate every imaginable topic. OpenAlex supplies scholarly clusters. Library of Congress Subject Headings supplies a broader authority vocabulary, including everyday interests, arts, history, places and composite subjects. Both have omissions, historical choices and updates.

Numeric space filling

Each record has a stable source identifier and a Morton address formed by interleaving four 16-bit integers. OpenAlex uses its domain, field, subfield and numeric topic IDs. Library subjects use a separate zero namespace and three parts of their numeric authority ID. Addresses are strings to avoid JavaScript integer rounding.

This provides deterministic numeric indexing and reversible coordinates. It does not turn categorical IDs into measured semantic distances. Empty numeric cells do not mean an unknown fact exists. The source hierarchy and its actual broader/narrower links remain the subject-navigation authority.

Which gaps can be measured?

• Access: a request for a particular subject page.
• Catalogue search: a server-computed match or no-match result; raw search text is not saved by passive observation.
• Collection gap: this site has no reviewed answer for an exact submitted question.
• Reported evidence problem: an explicit request says a source is missing or conflicting; it awaits review.
• Research result: an owner-reviewed sourced answer, with date, limits and revision.

A page visit, crawler user-agent, no-match query or library heading is insufficient to establish an external research gap, model identity, correct citation or ranking effect. Explicit reports remain private. No paid model or automatic fabricated answer is installed.

Inspect exact snapshot coverage · Tracking and privacy choices