Hypogeic

Definition

Hypogeic is a directional and jurisdictional term of the Tower's cartographic apparatus, denoting that which lies, opens, or is administered beneath a given reference plane. It is not synonymous with "underground," a word the Librarians reserve for incidents of structural collapse and have declined to extend to ordinary descent. An aperture, grotto, stair, or pooling surface is hypogeic relative to the floor from which it is addressed; the same feature may be superterranean when addressed from a lower floor, and frequently is, which is the origin of most standing disputes. The term appears in its modern technical sense no earlier than the Third Concordance, Annex 12, though earlier recensions use it loosely and with evident fatigue. Its opposite, Apogeic, is defined by the same annex and is considerably better behaved.

Scope and reference planes

The practical difficulty of hypogeic designation is the selection of a reference plane, and the Tower has never settled this to universal satisfaction. Two competing conventions are in force. The first, favoured by the Salt Flats Curatorial Authority, holds that the reference plane is the local floor datum — the walking surface of the numbered floor in question. Under this convention the Salt Grottoes beneath Floor 44 are hypogeic, and the matter ends there. The second convention, maintained by the Department of Structural Verifications, holds that the reference plane is the datum of the lowest floor from which the feature remains addressable in writing, which in practice means the feature's own address. Under this convention a feature that has been catalogued twice from two floors may be simultaneously hypogeic and apogeic, and frequently is. The Department accepts this without embarrassment. Its position is that contradiction in the record is a property of the feature, not of the record. A third convention, associated with the Western Salt-Corridor and never formally adopted, holds that the reference plane is tidal. Under it, hypogeic status is periodically conferred and withdrawn.

Hypogeic features of the Western Salt-Corridor

The Western Salt-Corridor is the type locality for hypogeic study, and the only region in which the term has acquired a dynamic rather than static sense. The corridor's grottoes are subject to cyclical expansion and contraction correlated with Tidal Librations, a phenomenon which raises the question of whether a space that grows is the same space. The Salt Flats Curatorial Authority has ruled that it is, on the grounds that the salt remains. The Department of Structural Verifications has filed a standing dissent. Survey parties working the corridor record depth in fathoms of descent and in fathoms of return, and these figures rarely reconcile. The discrepancy is conventionally attributed to the corridor; it is at least as conventionally attributable to the surveyors, who are given strong tea and a shorter shift.

Relation to Apogeic

Apogeic and hypogeic are complementary terms and are defined in a single clause of the Third Concordance, which reads, in full, that "that which is below is below, and that which is above is above, and the reader will know which by where they stand." The clause has been cited in support of opposing findings on four documented occasions, most recently in the matter of Verity's Span, where a single arch was found apogeic from the north and hypogeic from the south for eleven consecutive years before the matter was referred upward and, it is presumed, resolved. The Codicil of Petrified Voices records hypogeic addresses in a hand distinct from its apogeic entries, which has led to the persistent but unproven theory that the codex was maintained by two clerks working from opposite ends of the same shelf.

Administrative standing

Hypogeic designation carries consequential obligations. Features so designated fall under the corridor's survey regime and are subject to recertification whenever their address changes, which for tidal features is a standing obligation rather than an event. Non-compliance is uncommon; the penalties are old, dull, and have been applied twice. The term is also used figuratively in the Tower's administrative prose, with results the Department of Structural Verifications has described as "unhelpful but not actionable." A matter described as hypogeic in correspondence is one held below the level at which it can be settled — a usage that appears first in internal memoranda of the winter of the eighteenth recension and has since spread to filings where no spatial claim is intended at all.

"The hypogeic is not the hidden. It is the located, and located below, which is a different thing and a worse one."

— Third Concordance, Annex 12, §3

See also

• Tidal Librations
• Salt Grottoes
• Floor 44
• Apogeic
• Pulmonary Brine Pools