Correspondences

The ABS makes available an extensive range of correspondence files, in machine readable format, to mathematically convert statistical data to and from geographic regions when more accurate methods for coding data to the ASGS (e.g. point-in-polygon allocations and geocoding) are not available. As most ABS data relates to population, standard correspondences have a weighting calculated on the location of the population and use population data modelled to residential address locations.

Correspondences for converting data from ASGS Edition 3 to ASGS Edition 4 will be progressively made available as each ASGS Edition 4 structure is released.

To access correspondence files from ASGS Edition 3 refer to Correspondences.

A suite of correspondences will be created for each of the ASGS structures between ASGS Edition 3 (2021) and ASGS Edition 4 (2026). The correspondence file structure and associated details are described below.

File format

This product contains geographic correspondences supplied in machine readable .csv format.

File naming conventions

Population weighted grid correspondences supplied by the ABS have a standard naming convention applied. The example below relates to a correspondence where 2021 Statistical Areas Level 2 (SA2s) are being corresponded to Edition 4 (2026) SA2s.

File name: CG_SA2_2021_SA2_2026.csv

In each correspondence file, there are a set number of columns. Below is a list of these columns using SA2 as an example, along with descriptions of what information each column provides.

SA2_CODE_2021

This is the unique numerical code representing the FROM region, in this case it is the unique 2021 SA2 code.

SA2_NAME_2021

This is a textual label associated with the unique code of the FROM region, in this case it is the textual label for each 2021 SA2.

SA2_CODE_2026

This is the unique numerical code representing the TO region, in this case it is the unique 2026 SA2 code.

SA2_NAME_2026

This is a textual label associated with the unique code of the TO region, in this case it is the textual label for each 2026 SA2.

RATIO_FROM_TO

This field describes the Ratio of the FROM region that is being donated to the TO region. The Ratio is a figure between 0 and 1.

INDIV_TO_REGION_QLTY_INDICATOR

This field describes how well data is likely to be converted to the “TO” region. There are three values associated with the Individual to Region Quality Indicator:

• Good – the ABS expects that for this “TO” region the correspondence will convert data to a high degree of accuracy and the converted data will reflect the actual characteristics of the geographic regions involved.
• Acceptable – the ABS expects that for this “TO” region the correspondence will convert data to a reasonable degree of accuracy, though caution needs to be applied as the quality of the converted data will vary and may differ from the actual characteristics of the geographic regions involved.
• Poor – the ABS expects that for this “TO” region there is a high likelihood the correspondence will not convert data accurately and that the converted data should be used with caution as it may not reflect the actual characteristics of the geographic regions involved.

OVERALL_QUALITY_INDICATOR

An overall quality indicator is applied to each correspondence. The aim of this is to provide a reasonable idea of how well the correspondence will convert data across the whole of the correspondence. There are three values associated with the Overall Quality Indicator, and they are identical to those listed above for the Individual to Region Quality Indicator.

BMOS_NULL_FLAG

This is the acronym for the Below Minimum Output Size/Null values flag. The CSV file may contain records that are below a pre-set minimum output size (typically below a ratio of 0.01). These are records where the proportion of the “FROM” region that is being donated is very small and is deemed as being statistically insignificant. Records that fall into this category will be flagged by a specific code as described below.

Null values are records where part or all of a “FROM” region does not have a corresponding “TO” region, or vice versa. An example of when this may occur is when one geography dataset contains islands which are not included in the other dataset. If the correspondence contains Null records, they will be flagged by a specific code as described below.