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To be read in association with 2001 to 2006 Census Collection District Comparability Listing, Aug 2006(cat. no. 2919.0.55.001).

When comparing small area statistics at different points in time, it is important to take into account changes to the definitions of these areas. To aid time-series analysis, the ABS publishes the Australian Standard Geographic Classification (ASGC) on a yearly basis. The ASGC for census years includes a definition of Census Collection Districts (CD). A proportion of CD boundaries change between each census, and this fact sheet provides a description of the CD Comparability Listings that the ABS produces to facilitate the comparison of CDs.

Changes to Census Collection Districts

While Census Collection Districts are used to disseminate census data, they are primarily designed as a collection unit. To this end, there is a requirement to redefine their boundaries each census according to a range of enumeration criteria. In general, CD design aims to produce convenient areas for a single collector workload. CD design thus involves splitting of CDs where there has been strong population growth. Where population numbers are known to have declined, CDs may be amalgamated. Adjustment of the boundary between CDs may also occur where Local Government Area (LGA) or suburb boundaries have changed.

During CD design for the 2006 Census, a minimalist approach was taken. That is, where possible, the 2001 CD boundaries were retained. Approximately 20% of 2001 CDs were redesigned for the 2006 Census. However in 2006, for operational requirements, even where the geographic extent of a CD remained the same, the CD code may have changed. Users who wish to compare data between two or more censuses are faced with a difficult task. To facilitate comparisons between censuses at the Census Collection District level, the ABS has constructed a set of comparability lists. These lists allow users to make an association between CDs that define the same geographic area, but may have different CD codes. Also, where there has been a boundary change they provide information about the type and degree of change which occurred.

2006 Census CD Comparability Listing

For changes between the 2001 and 2006 Censuses, a single digit comparability code has been allocated to pairs of 2001 and 2006 CDs. The resultant listing, which includes all CDs for both 2001 and 2006, indicates the degree to which the boundary of a CD has changed between the 2001 and 2006 Censuses.

For changes between the 1996 and 2006 Censuses, pairs of 1996 and 2006 CDs have been assessed as either comparable or not comparable, and assigned a code.

Users should note that there are a number of entries in the Comparability Listing where one of the pair of CDs is shown as having a CD code of zero. Zero CD Codes represent Shipping or Water CDs that have either been deleted or newly created since 2001 and therefore have no corresponding CD to be linked to in the other Census year. In general this will not affect users as these CDs are excluded from most products.

The full 2001 to 2006 CD Comparability Listing is available on the ABS website (cat. no. 2919.0.55.001). The Comparability Listings for 1996-2001 and 1996-2001-2006 are available on request by contacting the Geography Section (geography@abs.gov.au).

The codes used in Comparability Listings are as follows:

Code	Description
1996 - 2006
0	2006 CD is comparable to the 1996 CD.
1	2006 CD is not comparable to the 1996 CD.
2001 - 2006
0	2006 CD is directly comparable to the 2001 CD.
1	Although a change to the CD boundary has been made between the 2006 and 2001 Censuses, the 2006 CD is comparable as there is no change to dwelling counts due to boundary change.
2	2006 CD is comparable within a 2% dwelling change limit. This means that a boundary change has occurred, but no more than 2% of the dwelling counts in the 2001 CD have been subtracted or added.
3	2006 CD is comparable within a 10% dwelling change limit. This means that a boundary change has occurred, but no more than 10% of the dwellings in the 2001 CD have been subtracted or added.
4	2006 CD is not directly comparable. A 2001 CD has been split into two parts, with the 2001 boundary containing two new 2006 CDs.
5	2006 CD is not directly comparable. A 2001 CD has been split into 3 or more parts, with the 2001 boundary containing three or more new 2006 CDs.
6	2006 CD is not comparable because of splits, amalgamations, or boundary variations, with no common boundaries being retained and there has been a change to dwellings of more than 10% of the 2001 CD.
7	2006 CD is not directly comparable because it is an amalgamation of two adjacent whole 2001 CDs into a new 2006 CD.
8	2006 CD is not directly comparable due to an amalgamation of three or more adjacent whole 2001 CDs into a new 2006 CD.
9	The 2006 CD has changed slightly when compared with the 2001 CD due to a change in the base map between censuses, for example, for roads, rivers or railway lines. The 2006 CD boundary follows the same features as in 2001, but the boundary has been realigned to follow the improved base map data. Although the shape of the 2006 CD may look quite different to the 2001 CD, for statistical purposes the two are comparable.

OTHER ASGC AREAS

Although the ABS makes annual changes to ASGC areas (excluding CDs), ASGC areas used for the 2006 Census are those as defined at 1 July 2006.

Where to locate information about changes to ASGC areas between Censuses

The publication Statistical Geography Volume 1 - Australian Standard Geographical Classification (ASGC) (cat. no. 1216.0) lists changes to ASGC areas. Appendix 2 of the 2006 Edition of the ASGC provides a summary of the changes to ASGC areas from the 2001 Census to the 2006 Census.

Census Geographic Areas

In order to assist clients who require data on the basis of non-ABS administrative areas, such as Commonwealth Electoral Divisions, Suburbs and Post Codes, the ABS creates CD-derived boundaries as a best fit approximation for which census data may be released. These CD-derived areas, known as Census Geographic Areas are designed to approximate the appropriate boundary current at the time of the 2006 Census, although in some cases they may represent an administrative boundary which came into effect shortly after the Census.

Census Geographic Areas remain effective until the next census, even though the boundary they represent may undergo changes in this period. For example, an electoral redistribution may occur.

Statistical Geography Volume 2 - Census Geographic Areas Australia (cat. no. 2905.0) contains a detailed explanation of the Census Geographic Areas and lists their codes and labels.