CODING INDEXES

Coding indexes enable data collected with a partial address to be linked to a geographic area. For ABS purposes, coding indexes are tables that list a geographic area against its most appropriate match in the ASGS. For example, a coding index will indicate a Locality and the SA2 it is most appropriately associated with based on the distribution of population within the locality. Table 1 shows an example of a Locality to SA2 coding index.

Table 1: Example of Locality to SA2 Coding Index
LOCALITY NAME	STATE	POSTCODE	SA2 MAINCODE 2011	SA2 NAME 2011
IRYMPLE	VIC	3498	215021395	Irymple
NICHOLS POINT	VIC	3501	215021395	Irymple
NICHOLS PT	VIC	3501	215021395	Irymple
EAST MILDURA	VIC	3500	215021397	Mildura
MILDURA	VIC	3500	215021397	Mildura
MILDURA EAST	VIC	3500	215021397	Mildura
MILDURA SOUTH	VIC	3500	215021397	Mildura
MILDURA WEST	VIC	3500	215021397	Mildura
SOUTH MILDURA	VIC	3500	215021397	Mildura
WEST MILDURA	VIC	3500	215021397	Mildura
HATTAH	VIC	3501	215021398	Mildura Region
KOORLONG	VIC	3501	215021398	Mildura Region
LINDSAY POINT	VIC	3496	215021398	Mildura Region
LINDSAY PT	VIC	3496	215021398	Mildura Region
MERINEE	VIC	3496	215021398	Mildura Region
MERINGUR	VIC	3496	215021398	Mildura Region
MERRINEE	VIC	3496	215021398	Mildura Region
NEDS CORNER	VIC	3496	215021398	Mildura Region
WARGAN	VIC	3496	215021398	Mildura Region
WERRIMULL	VIC	3496	215021398	Mildura Region
KARADOC	VIC	3496	215021399	Red Cliffs
RED CLIFFS	VIC	3496	215021399	Red Cliffs
SUNNYCLIFFS	VIC	3496	215021399	Red Cliffs

The coding index in Table 1 lists a series of Locality names, along with State and Australia Post postcode. For each Locality it then lists the associated SA2 Code and SA2 Name. In cases where users have unit record data that does not contain whole addresses, but does contain Suburb/Locality and Australia Post postcode information, an accurate match to the SA2 level of the ASGS can be obtained. In this instance the Australia Post postcode is important as Locality names are not necessarily unique, even within a State - the postcode aids in identifying the correct Locality.

Care should be taken when applying coding indexes, as the transformed areas may not be wholly within their associated ASGS region. Coding indexes do not apportion data - they assign whole areas to the most appropriate region within the new geography. As a general rule, small areas can be assigned more accurately than large areas.

During the development of the ASGS, SA2 boundaries were designed to reflect officially gazetted Suburb and Locality boundaries. As a result, if collection units contain this level of information, they can be accurately coded to the SA2 level of the ASGS. The ABS will supply this index free of charge, and it is available upon request through our Contact us page.

Similarly, coding indexes have been created that enable users to match postcode data to the SA4 and Greater Capital City Statistical Area (GCCSA) boundaries, as well as 2006 Remoteness Areas and 2011 Statistical Divisions (SD).

There are issues that users need to be aware of when using postcode data as the sole source of deriving a match to the ASGS however. Firstly, there is no definitive set of postcode boundaries available, as Australia Post does not maintain a definitive set of boundaries as a matter of course. Various organisations have created their own boundaries, but these can differ quite significantly from one dataset to another. Another issue is that postcodes do not cover the whole of Australia. Postcodes are also, in general, larger than Suburbs and as a result cannot be coded to the more detailed levels of the ASGS. As a result, these coding indexes will only be released at the SA4 and GCCSA levels as the quality of these coding indexes at this level are deemed to be acceptable.