Correspondences

The ABS makes available an extensive range of correspondence files, in machine readable format, to help users to mathematically convert statistical data to and from geographic regions. As most ABS data relates to population, standard correspondences have a weighting calculated on the location of the population and uses population data modelled to residential address locations.

A larger set of historical ASGC and ASGS geographic correspondences are available through data.gov.au, an open data portal. The ABS uses this open data portal to help make ASGS output products accessible to a wider audience. These products can be located on data.gov.au through the ABS Geospatial Solutions page. Alternatively, search for the 'year', along with the key words such as ‘correspondence’, ‘ASGS boundaries’ or ‘coding index’ depending on the product of interest.

To access correspondence files from previous editions of the ASGS, refer to the following links:

Main Structure and Greater Capital City Statistical Areas

Remoteness Structure

Significant Urban Areas, Urban Centres and Localities, Section of State

Indigenous Structure

Non ABS Structures

A suite of correspondences will be created for each of the ASGS structures between ASGS 2016 and ASGS Edition 3 (2021). 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

Grid based correspondences supplied by the ABS have a standard naming convention applied. The example below relates to a correspondence where 2016 Statistical Areas Level 2 (SA2s) are being corresponded to Edition 3 (2021) SA2s.

File name: CG_SA2_2016_SA2_2021.csv

In each correspondence file, there are a set number of columns. Below is a list of these columns, along with descriptions of what information each column provides the user:

SA2_MAINCODE_2016
This is the unique numerical code representing the FROM region and in this case, the unique 2016 SA2 code.

SA2_NAME_2016
This is a textual label associated with the unique code of the FROM region, in this case it is the textual label for each 2016 SA2.

SA2_MAINCODE_2021
This is the unique numerical code representing the TO 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 TO region, in this case it is the textual label for each 2021 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 Quality Indicator:

Good – The ABS expects that for this “TO” region the correspondence will convert data to a high degree of accuracy and users can expect 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 many of the geographic regions involved.

OVERALL_QUALITY_INDICATOR

An overall quality indicator is applied to each correspondence. The aim of this is to provide users with 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 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.

BMOS_NULL_FLAG Codes

 0 – Record is not below the specified minimum output size and has both a “FROM” and “TO” region present.

1 – Record is below the specified minimum output size, but both a “FROM” and “TO” record are present.

2 – Record has a null “TO” unit.

3 – Record has a null “FROM” unit.

4 – Record is below the specified minimum output size and the “TO” unit is null.

5 – Record is below the specified minimum output size and the “FROM” unit is null.