##  [Vertical Datum](/vertical-datum-0) 

 Definition

The explicitly defined reference surface or zero‑elevation level (geodetic or project‑local) from which vertical positions, heights and depths are measured and reported in field recording.

 

 

 

 

 

 





## Principle

Principle

Vertical measurements are meaningful only relative to a stated vertical datum; without the datum, numeric elevations lack an unambiguous reference and cannot be reliably integrated with other vertical data.

 

 

 

 

 





## Demonstration

Demonstration

Illustrative scenario: Situation — A report lists feature elevations. Recognition — The archaeologist specifies that all elevations refer to the project's temporary datum, itself tied to a national vertical datum by a surveyed benchmark. Action — Other researchers convert elevations to their GIS by applying the documented offset. Consequence — Elevations integrate correctly across datasets because the datum relationship is recorded.

 

 

 

 

## Misapplication

Misapplication

Reporting elevations without naming the vertical datum or its relationship to any national or project datum; the semantic error is treating elevation values as absolute when their reference surface is unspecified.

 

 

 

 

 





## Consequence

Consequence

Omitting the datum produces ambiguities when datasets are merged, can introduce systematic elevation offsets, and may invalidate comparisons of depth‑dependent analyses such as sediment accumulation or construction phases.

 

 

 

 

## Reversal

Reversal

For analyses confined to relative stratigraphy within a single, short‑term excavation area, a project‑local datum that is not referenced to a national system may be sufficient; conversely, long‑term monitoring, cross‑site comparison and integration with topographic data require a geodetically traceable vertical datum.

 

 

 

 

 





## Boundary

Boundary

Clearly within: elevations explicitly stated as referenced to a named vertical datum (national or project) with documented tie points. Boundary case: elevations given relative to an unnamed 'site zero' recorded only in field notes. Clearly outside: qualitative depth descriptions (e.g., 'deep', 'shallow') without numeric elevation or datum.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Absolute geodetic anchoring for interoperability ↔ sufficiency of relative stratigraphic levels for intra‑site interpretation and efficiency.

 

 

 

 

 





## Synthesis

Synthesis

A vertical datum is the necessary semantic anchor that gives elevation numbers meaning; specifying its identity and any offsets is essential for integrating, comparing and reusing vertical data across surveys, projects and time.