height above mean sea level
Enable an agent to interpret, compare and use a reported vertical position relative to mean sea level while preserving its reference surface, measurement context and uncertainty.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
recalled by Codex without web access - no source was read
Researched by: Codex
Purpose and description
Enable an agent to interpret, compare and use a reported vertical position relative to mean sea level while preserving its reference surface, measurement context and uncertainty.
Height above mean sea level is the vertical position of a point relative to a specified sea-level-based reference surface or vertical datum, conventionally positive upward.
It can be Interpret a signed height against its documented sea-level reference.; Request missing datum, target-point or epoch information before comparing elevations.; Determine whether two reported heights share a compatible reference and uncertainty basis.; Transform a height using an applicable documented transformation while retaining the original value.; Assess whether a reported height has sufficient accuracy and reference information for a stated task.; Flag apparent height changes that may result from reference changes or measurement differences..
Distinguishing features
Its zero is a stated mean-sea-level reference or associated vertical datum, rather than the ground immediately beneath the measured point.
A value labelled altitude or elevation qualifies only when its vertical reference is established; the label alone does not establish mean-sea-level referencing.
A raw ellipsoidal height is not interchangeable with height above mean sea level without an identified relationship between the reference surfaces.
A negative value denotes a point below the adopted reference zero and is a valid height value.
A sea-level reference based on averaging or a datum realisation differs from the instantaneous sea surface at a particular tide.
Scope
+ The point or surface whose height is reported
+ The meaning and realisation of the mean-sea-level reference
+ Height value, unit, sign convention and uncertainty
+ Measurement or derivation method and supporting reference information
+ Spatial and temporal applicability of reported heights
+ Conditions for comparing or transforming sea-level-referenced heights
- Latitude, longitude and complete positioning systems except as needed to interpret height
- Height above local ground or a building's base
- Ellipsoidal height as an independent quantity
- Instantaneous tide level and sea-level change as phenomena
- Terrain morphology and landform classification
- Flood prediction, aviation clearance and engineering design decisions
Characteristics
- Reported height
- Signed length with an explicit unit, commonly metres or feet Provides the vertical quantity while preventing unit and sign ambiguity.
- Height-bearing point
- Identified point or surface, including horizontal location and the relevant part of an object Distinguishes a summit, ground surface, antenna reference point or other measurement target.
- Vertical reference
- Named datum, local sea-level reference or explicitly unknown reference Establishes what zero means and whether another height is comparable.
- Height-system interpretation
- Declared height-system type, locally defined sea-level height or unspecified Prevents the phrase above mean sea level from concealing different technical definitions.
- Reference realisation
- Applicable benchmark network, reference model, version or local averaging record Connects the stated reference to a reproducible practical realisation.
- Observation and reference times
- Observation date, reference epoch and sea-level averaging interval where applicable Separates when the point was measured from when its reference was established.
- Determination method
- Levelling, satellite-derived conversion, calibrated barometry, mapped or modelled estimate, other documented method or unknown Identifies which corrections, assumptions and error sources require examination.
- Height uncertainty
- Length-valued uncertainty with its statistical meaning and included error contributions Supports defensible comparisons and prevents displayed precision from being mistaken for accuracy.
- Interpretation readiness
- Reference established, reference ambiguous, transformation required or inadequate for intended use Makes missing reference information actionable.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 5 bundles · 9 layers · 17 findings · 25 questions.
Meaning of sea-level height Establishes what quantity the expression height above mean sea level denotes in the reporting context.
The everyday expression does not by itself identify a precise vertical reference or height-system definition.
Height-bearing target
Identifies the point represented by the reported vertical position.
Specified height point
Interpretation requires knowing which point or surface carries the height, including any offset between the instrument and the intended target.
- Does the value describe ground, a summit, a water surface, an instrument reference point or another explicitly identified point? definition
- Which instrument, antenna or surface offsets were applied to obtain the target point's height? measurement
Reference-sensitive meaning
Separates sea-level-referenced height from neighbouring vertical quantities.
Declared height interpretation
Terms such as elevation and altitude require contextual interpretation; their wording alone does not establish that a value is referenced to mean sea level.
- How does the reporting authority define mean sea level and the associated height quantity? definition
- What evidence distinguishes this value from ellipsoidal height, height above ground, pressure altitude or instantaneous water level? boundary
Sea-level reference realisation Records how the adopted reference zero is defined and made available for measurement.
Two reports can both say above mean sea level while using different reference surfaces or datum realisations.
Reference zero
Identifies the authority and definition behind the adopted sea-level reference.
Traceable reference zero
A usable interpretation identifies the adopted vertical datum or local sea-level definition rather than treating mean sea level as a self-explanatory universal zero.
- Which named vertical datum or local sea-level definition supplies zero for this height? provenance
- If zero comes from local sea-level observations, which station, averaging interval and processing definition established it? measurement
Practical reference access
Connects the reference definition to benchmarks, models or other means used to determine the height.
Reference realisation and coverage
The model needs the particular reference realisation used and its applicable area and time, including relevant benchmark or reference-model versions.
- Which benchmark identifiers, reference-model version or other realisation connected the observation to the adopted datum? provenance
- Is that realisation applicable at the target location and relevant epoch? boundary
Height determination and quality Explains how the reported height was obtained and what confidence its value supports.
A surveyed height, converted satellite height and map estimate need different evidence before an agent can rely on them.
Determination chain
Traces observations and corrections to the reported sea-level-referenced value.
Documented height derivation
The derivation should identify the measured quantity, its original reference and the corrections or transformations producing the reported height.
- Was this height obtained through levelling, satellite observations, calibrated barometry, a terrain dataset or another method? measurement
- Which original observations, calibration records and conversion steps support the reported sea-level reference? provenance
Uncertainty and resolution
Separates reporting precision from the uncertainty of the height and its reference.
Interpretable height uncertainty
Uncertainty must be interpretable in length units with stated statistical meaning and scope; decimal places alone cannot establish accuracy.
- What uncertainty is reported, with what confidence convention, and does it include reference-model and transformation errors? measurement
- How do rounding, terrain sampling or horizontal-position uncertainty affect the height assigned to this particular point? measurement
Comparison, change and use Governs comparisons, transformations and interpretations of height differences.
Numerical differences only support conclusions when target points, reference systems, times and uncertainties are understood.
Reference-compatible comparison
Determines when heights can be compared directly and when a transformation is necessary.
Comparison and transformation conditions
Before comparing heights, an agent must establish compatible units and references or use a documented transformation with adequate coverage and uncertainty.
- Do the values use compatible units, sign conventions, height systems and datum realisations? boundary
- If a transformation is required, which documented operation applies here and what additional uncertainty does it introduce? action
Temporal and task interpretation
Relates apparent height changes and practical use to observation times and evidence quality.
Supported height conclusions
A difference between reported heights can reflect point movement, reference changes or measurement effects; intended use determines the evidence and accuracy required.
- For repeated measurements, what evidence separates movement of the same target point from datum revisions, reference changes and measurement uncertainty? measurement
- Does the height's reference, age and uncertainty support the intended task, or must the agent obtain a better measurement or additional context? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Check these first
Recalled without web access and unsourced; every item is a lead to verify.
- The registry supplies no sense; this description covers the geodetic quantity and its ordinary mapping usage.
- Mean sea level is not one universally realised zero surface; identify the datum, height type and relevant epoch before comparing values.
- Normal heights reference a quasigeoid, not a gravity equipotential surface; their inclusion reflects practical usage of sea-level-based national height systems.
- Which of these check these first hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Kinds and varieties
Recalled without web access and unsourced; every item is a lead to verify.
- Orthometric height, referenced to the geoid
- Normal height, referenced to the quasigeoid
- Height referenced to a local mean-sea-level datum
- Which of these kinds and varieties hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Identifiers and schemes
Recalled without web access and unsourced; every item is a lead to verify.
- EPSG Dataset - EPSG:<numeric code> - Codes identify particular vertical coordinate reference systems and datums; there is no single code for height above mean sea level in general.
- Which of these identifiers and schemes hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Standards and regulation
Recalled without web access and unsourced; every item is a lead to verify.
- ISO 19111, Geographic information - Referencing by coordinates, issued by ISO
- International System of Units (SI), maintained by the BIPM, specifies the metre as the unit of length
- Which of these standards and regulation hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Real-world use
Recalled without web access and unsourced; every item is a lead to verify.
- Mapping terrain elevations and mountain summit heights
- Surveying and establishing engineering control
- Describing aerodrome elevations and aircraft altitudes
- Modelling drainage, flooding and coastal inundation
- Referencing environmental observations and infrastructure elevations
- Which of these real-world use hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Typical measurements
Recalled without web access and unsourced; every item is a lead to verify.
- Height relative to the declared vertical datum - Negative below the reference surface, zero on it, and positive above it; the applicable range depends on the object and application - metre (m); feet are also used
- Which of these typical measurements hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Failure modes and hazards
Recalled without web access and unsourced; every item is a lead to verify.
- Combining elevations from different vertical datums without transformation creates systematic offsets.
- Treating GNSS ellipsoidal height as height above mean sea level can produce substantial errors.
- Using instantaneous sea level or an unspecified tidal datum as mean sea level misstates the reference.
- Confusing barometric altitude with surveyed elevation introduces errors from pressure and atmospheric conditions.
- Ignoring land motion, datum epoch or sea-level change can compromise precise comparisons over time.
- Which of these failure modes and hazards hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Regional variation
Recalled without web access and unsourced; every item is a lead to verify.
- National height systems use different reference tide gauges, averaging periods and datum realisations.
- Some national systems use orthometric heights, while others use normal heights.
- Metres predominate in mapping and surveying internationally; feet remain common in aviation and some national practices.
- Which of these regional variation hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Recalled without web access and unsourced; every item is a lead to verify.
- Ellipsoidal height - References a mathematical ellipsoid rather than a sea-level-based vertical surface.
- Height above ground level - References the local ground surface rather than a vertical datum associated with sea level.
- Mean sea level - Is an averaged sea-surface level used in defining references, rather than the height of another point.
- Geoid - Is an equipotential surface of Earth's gravity field used as a reference for orthometric height, rather than a height value.
- Elevation - Usually describes the height of a terrestrial point; its reference datum must still be specified and need not be mean sea level.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of height above mean sea level this model covers, and on what evidence? provenance
What the second pass must settle
- Which authoritative definition should anchor this registry entry, and how should it accommodate technical height systems commonly described as above mean sea level?
- Which neighbouring registry or world-model entries already own vertical datums, ellipsoidal height, orthometric height and normal height, so this model can link to them without duplicating their scope?
- What minimum reference metadata should be required before an informal above-mean-sea-level value is considered suitable for quantitative comparison?
- Which documented transformations and reference models should agents recognise for the jurisdictions and datasets where this model will be used?
- How should task-specific accuracy requirements govern the treatment of old observations, moving target points and revised vertical reference realisations?