The Australian Bureau of Statistics
has divided Australia
into several perfectly concorded spatial
areas, allowing for statistics to be recorded and reported from different levels of geographic detail. The spatial units in common use are Census Collection District
s (CCD), Statistical Local Area
s (SLA), Statistical Subdivision
s (SSD), Statistical Division
s (SD) and the individual States and Territories (S/T).
Except for state and territory boundaries, they generally do not correspond with other spatial units in common use, such as state/federal electorates, local government areas and postal areas. Amongst themselves they do not overlap nor fail to cover all of Australia, including its external territories (except our slice ofAntarctica).
Census Collection District
At the smallest level are Census Collection Districts. There were 37,209 CDs defined in the 2001 Australian census. The number of people reported in a CD is generally too small to be used as a statistically significant sample, and there are privacy limits in place for reporting results at CD level. The rules the ABS uses for defining CDs are:
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.
CDs in aggregate must cover the whole of Australia (as defined in Chapter 1, p. 5) without gaps or overlaps.
The ABS has special CD categories to record dense pockets of people that appear on Census
night in the middle of nowhere - such as mining
personnel and transient indigenous communities. These CDs prevents skewing statistics for the larger, emptier SLA it forms part of. There is also the category of Off-shore, shipping and migratory
CDs to cover people who were caught spending on Census
night on oil rig
s, harboured yachts, flying the red eye
special or anywhere else physically difficult to enumerate. These special CDs are aggregated together in higher level spatial units.
Each CD is given a unique six-number code.
Statistical Local Area
Many CDs form a Statistical Local Area. They are the smallest spatial unit worth disseminating as a reliable measure. In 2005 there were 1,415 SLAs in Australia including one SLA for each of the three territories of Jervis Bay, Christmas Island and Cocos (Keeling) Islands.
SLAs concord with the boundaries of incorporated local government areas (LGA) where possible. However where an LGA encroaches over two or more SSDs, or is composed of significantly dissimilar population or economic settlement patterns, additional SLAs may be deliniated. Those large portions of Australia that are not part of any local government area or have any significant economic activity, such as Arnhem land or the non-urban parts of the Australian Capital Territory are designated as 'unincorporated' SLAs.
SLAs are named after the LGA they are based on, with the suffix of (S), (T) or (C) to denote if the LGA is a shire, town or city. If an LGA has several SLAs, then each SLA is denoted with 'Part A', 'Part B' etc.
SLAs also have four-number codes (since there are several SLAs sharing the same name in Australia; indeed the city of West End is featured twice in Queensland, as suburbs in Brisbane and Townsville).
SSDs are defined as socially and economically homogeneous regions characterised by identifiable links between the inhabitants. This definition therefore can apply to a large regional town (eg: Ballarat SSD), or to several closely clustered LGAs (eg: Sunshine Coast SSD). An SSD boundary may split the LGA into parts with each part of the LGA forming part of the relevant SSD.
There were 207 SSDs in Australia in 2005. They are coded as unique five-digit numbers.
The largest and most stable spatial unit within a state or territory, SDs are only changed every 15-20 years. There are 66 SDs in Australia, and they are defined by the ABS in conjunction with local states and territories to cover homogeneous and highly interdependent regions. For example, Adelaide and the Kimberley are SDs.
All these CDs, SLAs, SDs and SSDs neatly accord with themselves and the state or territory they belong in. The ABS aggregates Jervis Bay, Christmas Island and Cocos (Keeling) Islands and 'other'.
SDs are coded as three digit numbers.
Outside this classification are UCLs (Urban Centre localities), which are clusters of contiguous CDs that share a high population density, and together have a non-farm population of 200 or greater. They may span across any number of spatial units described here. Actually the method to deliniate a UCL is an adaptation of a technique authored in 1965 by Dr GJR Linge from the Australian National University and goes into detail too verbose to be mentioned here.