Landonline: Datum

**Please read:** This table is part of the comprehensive Full Landonline Dataset and is designed for use only by data professionals who require the complex version of our property ownership and boundary data for advanced uses.
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A Datum is a complete system for enabling Coordinates to be assigned to Nodes. A datum is prescribed by the appropriate authority from which it derives its validity. All Coordinates will be in terms of a Datum. A Datum also provides a spatial standard for the alignment of Reduced Observations via a Datum Calibration. Most Reduced Observations are Datum dependent but there are specific Reduced Observation types which are Datum independent. The Datum entity contains information about the official geodetic Datum used in Land Information NZ databases and other important Datum’s used to spatially reference source data (e.g.. Reduced Observations) or output data or products (e.g.. Coordinates, Digital Cadastral Database, topographic maps, hydrographic charts, etc). The Datum entity includes objects which, strictly, are reference frames rather than datum’s but the distinction is a fine technical point which is of no great consequence. The Datum entity includes vertical reference surfaces such as leveling datum’s, various tidal surfaces including Mean Sea Level, the geoid, datum ellipsoids, etc. For a Datum to maintain accuracy over a significant area it must be geodetic. Examples of non-geodetic datum’s are the Old Cadastral Datums. These do not account for the curvature of the earth and therefore can only maintain accuracy over a limited part of the earth's surface.

Please refer to the [LDS Full Landonline Data Dictionary and Models](https://data.linz.govt.nz/document/95) for detailed metadata about this table.