6. Data Quality¶
6.1. Positional accuracy¶
G-NAF is a concerted effort to deliver the best possible geocoded national address dataset for Australia. The magnitude of this dataset, the complexity of its content, and the multiplicity of its sources, means that there is ongoing requirement to improve the content, quality and coverage of G-NAF. All addresses in G-NAF contain a locality geocode. This geocode will generally be at the centre of the locality. If the name of the street in the address can be matched to one in the locality, then another geocode is added at the centre of the street within that locality. This is generally referred to as the street locality geocode. If the address is provided with coordinates or can be matched to one that already exists, then a third geocode will be added, placing the address inside the relevant property. This is generally referred to as the address site geocode.
6.2. Coordinates Referencing the GDA 2020 Datum¶
From the November 2019 publication, coordinates in G-NAF are available referencing the GDA 2020 datum. These coordinates are produced using a coordinate transformation from GDA 94 using the following parameters.
6.3. Attribute accuracy¶
Attribute accuracy is determined from rigorous standardisation processes and matching of the contributor datasets together with matching of addresses against the gazetted localities from Geoscape’s Administrative Boundaries and Roads datasets.
6.3.1. Address mesh block integration¶
G-NAF has a mesh block ID allocated to every address, where available. This includes addresses that have a geocode allocated at a street-locality and locality level where a single mesh block cannot be identified. A coding table (MB_MATCH_CODE_AUT) lists the codes describing the level of matching to mesh blocks.
The ABS recommends that G-NAF addresses associated with locality (and street) level geocode locations be associated with SA2 level units (ASGS units built up from SA2’s). While there is a strong alignment between gazetted suburb and locality boundaries, there are situations where SA2 boundaries split localities. In these circumstances, an unknown proportion of the addresses associated with the locality centroid will be coded to an incorrect SA2.
6.3.2. Allocation of postcodes¶
Postcodes are included in G-NAF at the address record level (i.e. postcode field in the respective ADDRESS_DETAIL tables). Geoscape allocates a postcode to every address and is based on the gazetted suburb/locality. The inclusion of a postcode in G-NAF is primarily based on the most commonly used postcode for all the addresses within in each gazetted suburb/locality. One of the exceptions is the addresses located in the area allocated to postcode 3004 for St Kilda Road, where the majority of addresses would be in the suburb of MELBOURNE.
Postcodes are used by Australia Post to facilitate the efficient processing and delivery of mail. There is no mandatory requirement for inclusion of a postcode in an address (AS4590).
6.4. Logical consistency¶
The dataset data structure has been tested for conformance with the data model.
6.5. Completeness¶
Completeness is an assessment of the extent and range of the dataset with regard to the completeness of coverage, completeness of classification and completeness of verification. The Data Maintenance section provides more information about the completeness of the dataset based on the processing steps.
6.5.1. Dataset coverage¶
National
6.5.2. Features¶
6.5.2.1. Addresses included¶
G-NAF aims to include all physical addresses in circulation by using multiple sources. The physical addresses in G-NAF are used to label land parcels and properties as well as for locating assets such as ATMs, tree plantations, reserves and substations.
6.5.2.2. Attribute completeness¶
All mandatory attributes for each object are populated. Some attributes are not populated but have been included in the data model to assist with the alignment with relevant standards.
The process of collating addresses varies across the contributors supplying data to G-NAF. Therefore, the attributes supplied can vary, but Geoscape will attempt to populate attributes based on the available information from the contributors.
6.5.2.3. Quality scope¶
The attribute accuracy is in scope for all areas in G-NAF.