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CDs are designed for use in census years for the collection and dissemination of Population Census data. In non-census years, CDs are undefined. In aggregate, CDs cover the whole of Australia (as defined in Chapter 1) without gaps or overlaps.

The CD is the smallest spatial unit in the ASGC. CDs aggregate to form the larger spatial units of SLAs in the Main, Statistical Region, Statistical District and LGA Structures, SOS in the SOS Structure, Urban Centres and Localities in the UC/L Structure and Remoteness Areas in the Remoteness Structure. Aggregation of SLAs in turn forms the remaining spatial units in the ASGC. Therefore, in census years, the CD is the common denominator which integrates all classification structures in the ASGC (see diagram 3, Chapter 1).

The traditional concept of a CD is that it defines an area that one census collector can cover, delivering and collecting census forms, in about a ten-day period. However, in the interests of comparability between censuses, this criterion is no longer strictly observed. In the 2001 edition, many urban CDs are of a size such that census collectors may be allocated more than one CD. In urban areas CDs average about 220 dwellings. In rural areas the number of dwellings per CD reduces as population densities decrease. By design, CD boundaries do not cross SLA (and thus LGA) boundaries. Therefore, an aggregation of CDs covers the administrative area of a local government.

For the 2001 Census, 37,209 CDs are defined throughout Australia. A listing of CDs within SLAs by S/T is included in this edition at Appendix 5.

Delimitation of CDs

For the 2001 Census, the following criteria were used for delimiting CDs:

• CDs should be consistent with the requirements of a collector’s workload and be a useful spatial unit providing the building blocks capable of aggregation into broader level ASGC spatial units;
  
  
• the area and population delimited by a CD boundary must not be so great that one collector cannot deliver and collect census forms within about ten days;
  
  
• the chosen CD boundaries should, if possible, be readily identifiable on the ground, be defined in terms of permanent features, follow the centre of a road or river if these features are used and should delimit CDs which conform to existing and proposed land uses. The use of major roads as CD boundaries in rural areas should be avoided where possible, i.e. to minimise splitting of identifiable rural localities;
  
  
• CDs should conform where possible to existing/gazetted suburb boundaries. CDs must not cross SLA boundaries and, as a consequence, any other ASGC spatial unit boundary;
  
  
• CDs should not be designed in such a way as to make them confidential for publication of data. Accordingly, a CD should contain, where possible, at least 100 persons at the next census. For dissemination purposes, Indigenous Community CDs will have a limit of 80 persons; and
  
  
• CDs in aggregate must cover the whole of Australia (as defined in Chapter 1) without gaps or overlaps.

• Indigenous Community CDs;
• Defence Establishments CDs;
• Mining or Construction towns or camps CDs; and
• Major Waterways CDs.