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Accuracy statements and technical information

Find out about the data model, accuracy statements and technical information about the NZTopo database.

Object orientated data model

NZTopo uses an object orientated (OO) data model. Real world entities are abstracted and held as objects where each object belongs to only one class. This means that an OO database more closely resembles the real world than a relational system – it has direct correspondence between the way entities are perceived and the data model that represents them. It is also more complex, however.

Real-world entities and abstract concepts can be modelled in terms of their shape, behaviour, location, relationships with other objects, and other properties.

The OO database model is based on several concepts:

  • Objects are grouped into classes.
  • Values (attributes) may be defined for each class. Values are the information that can be retrieved for an object.

NZTopo is stored in 1Spatial's GOTHIC Lamps2 Geographic Information System (GIS).

Accuracy statements

NZTopo data (1:50,000 scale)

Complies with the following statement of planimetric (x,y) accuracy: 90% of well-defined points are within +/-22metres.

Complies with the statement of vertical (z) accuracy: 90% of well-defined points are within +/-10 metres.

NZTopo data (1:250,000 scale)

Complies with the following statement of planimetric (x,y) accuracy: 90% of well-defined points are within +/-150metres.

Complies with the statement of vertical (z) accuracy: 90% of well-defined points are within +/-50 metres.

Technical information

NZTopo data (1:50,000 scale)

  • Data size: The NZTopo base data is approximately 3.5 gigabytes (zipped).
  • Number of features: Approximately 5,800,000 real world objects make up over 140 feature types that populate this database.
  • Source data: NZTopo base data is the data used in the production of the Topo50 map series.
  • Completeness: Spatial and attribute data capture is complete. Data currency is being maintained on a Topo50 sheet basis from digital imagery.

NZTopo data (1:250,000 scale)

  • Data size: The NZTopo base data is approximately 400 megabytes.
  • Number of features: Approximately 300,000 real world objects make up over 50 feature types that populate this database.
  • Source data: NZTopo (1:250,000 scale) base data is generalised from the 1:50,000 scale NZTopo base data.