National Geodetic Vertical Datum of 1929

E859786

United States vertical reference system geodetic reference system vertical datum

The National Geodetic Vertical Datum of 1929 is an older United States vertical reference system used to define elevations above sea level before being superseded by NAVD 88.

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All labels observed (6)

Label	Occurrences
National Geodetic Vertical Datum of 1929 canonical	4
NGVD 29	2
NGVD 88	1
NGVD29	1
National Geodetic Vertical Datum of 1929 (NGVD 29)	1
Sea Level Datum of 1929	1

How this entity was disambiguated

This entity first appeared as the object of triple T10378052 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.

NED1 Entity disambiguation (via context triple) gpt-5-mini-2025-08-07

Target entity: National Geodetic Vertical Datum of 1929
Context triple: [NAVD 88, replaced, National Geodetic Vertical Datum of 1929]

A. Newlands Reclamation Project
The Newlands Reclamation Project is one of the earliest U.S. federal irrigation projects, designed to divert water from the Truckee and Carson Rivers to transform arid Nevada lands into productive agricultural areas.
B. The Basin
The Basin is a popular, sheltered swimming and snorkeling beach on Rottnest Island in Western Australia, known for its clear turquoise water and white sand.
C. The Basin
The Basin is the common nickname for the Basin Reserve, a historic cricket ground and major sporting venue in Wellington, New Zealand.
D. The Basin
The Basin is a naturally formed granite pothole and popular scenic attraction along the Pemigewasset River in Franconia Notch, New Hampshire.
E. Great Stone Dam
The Great Stone Dam is a historic 19th-century granite dam in Lawrence, Massachusetts, built to harness the Merrimack River for industrial waterpower and central to the city’s mill-era development.
F. None of above. chosen
G. Unsure - the case is ambiguous/there is not enough information to decide.

NED2 Entity disambiguation (via description) gpt-5-mini-2025-08-07

Target entity: National Geodetic Vertical Datum of 1929
Target entity description: The National Geodetic Vertical Datum of 1929 is an older United States vertical reference system used to define elevations above sea level before being superseded by NAVD 88.

A. Newlands Reclamation Project
The Newlands Reclamation Project is one of the earliest U.S. federal irrigation projects, designed to divert water from the Truckee and Carson Rivers to transform arid Nevada lands into productive agricultural areas.
B. The Basin
The Basin is a popular, sheltered swimming and snorkeling beach on Rottnest Island in Western Australia, known for its clear turquoise water and white sand.
C. The Basin
The Basin is the common nickname for the Basin Reserve, a historic cricket ground and major sporting venue in Wellington, New Zealand.
D. The Basin
The Basin is a naturally formed granite pothole and popular scenic attraction along the Pemigewasset River in Franconia Notch, New Hampshire.
E. Great Stone Dam
The Great Stone Dam is a historic 19th-century granite dam in Lawrence, Massachusetts, built to harness the Merrimack River for industrial waterpower and central to the city’s mill-era development.
F. None of above. chosen

Statements (49)

Predicate	Object
instanceOf	United States vertical reference system ⓘ geodetic reference system ⓘ vertical datum ⓘ
abbreviation	NGVD 29 ⓘ linked to: National Geodetic Vertical Datum of 1929
alsoKnownAs	NGVD29 ⓘ linked to: National Geodetic Vertical Datum of 1929 National Geodetic Vertical Datum of 1929 (NGVD 29) ⓘ linked to: National Geodetic Vertical Datum of 1929
appliesToRegion	Alaska ⓘ Canada (limited use) ⓘ linked to: Canada Mexico (limited use) ⓘ conterminous United States ⓘ linked to: contiguous United States
basedOn	mean sea level observations at 26 tide gauges in the United States and Canada ⓘ
coordinateSystemType	vertical reference system ⓘ
country	United States ⓘ linked to: United States of America
datumType	orthometric height datum ⓘ
definedBy	network of geodetic leveling observations ⓘ
differenceFrom	NAVD 88 has spatially varying offsets relative to NGVD 29 ⓘ
documentationBy	NOAA National Geodetic Survey ⓘ linked to: National Geodetic Survey National Oceanic and Atmospheric Administration ⓘ
epoch	1929 ⓘ
establishedBy	National Geodetic Survey ⓘ U.S. Coast and Geodetic Survey ⓘ linked to: United States Coast Survey
establishedIn	1929 ⓘ
formerName	Sea Level Datum of 1929 ⓘ linked to: National Geodetic Vertical Datum of 1929
hasIssue	did not account for later improvements in gravity data ⓘ inconsistencies in mean sea level between tide gauges ⓘ
heightType	orthometric height ⓘ
maintainedBy	National Geodetic Survey ⓘ
partOf	National Spatial Reference System ⓘ
reasonForReplacement	need for a more accurate and consistent vertical datum ⓘ
referenceSurface	mean sea level as determined in 1929 ⓘ
referenceTo	tide gauge observations at multiple tide stations ⓘ
relatedTo	North American Datum of 1927 ⓘ
replacedInPracticeBy	NAVD 88 ⓘ
status	superseded ⓘ
supersededBy	NAVD 88 ⓘ North American Vertical Datum of 1988 ⓘ
unitOfMeasure	foot ⓘ meter ⓘ
usedBy	cartographers ⓘ civil engineers ⓘ federal agencies in the United States ⓘ state and local governments in the United States ⓘ surveyors ⓘ
usedFor	defining elevations above mean sea level ⓘ
usedIn	engineering surveys ⓘ floodplain mapping ⓘ hydrologic studies ⓘ topographic mapping ⓘ
usedUntil	late 20th century ⓘ

How these facts were elicited