Collection District (CD)
The Census Collection District (CD) is the second smallest geographic area defined in the Australian Standard Geographical Classification (ASGC), the smallest being the Mesh Block. The CD has been designed for use in the Census of Population and Housing as the smallest unit for collection and processing. For the 2006 Census, CDs will also be the basis of output for most data, the exception being some Place of Work destination zones and population counts for Mesh Blocks. For 2006, CDs also serve as the basic building block in the ASGC and are used for the aggregation of statistics to larger Census geographic areas.
A CD is represented by a unique seven digit code. For the 2006 Census, there is an average of about 225 dwellings in each CD. In rural areas, the number of dwellings per CD generally declines as population densities decrease.
CDs are defined for each Census and are current only at Census time. For the 2006 Census, there are about 38,200 CDs throughout Australia (this includes the other territories of Christmas and Cocos (Keeling) Islands and Jervis Bay).
The criteria for the design of CDs for the 2006 Census are as follows:
- CDs should be consistent with both their role as a useful spatial unit and building block capable of aggregation into broader level ASGC spatial units and with the collectors' workload requirements.
- The chosen CD boundaries should, if possible, be readily identifiable on the ground and 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 is avoided, where possible, to minimise splitting of identifiable rural localities.
- CDs should conform where possible to existing/gazetted suburb boundaries, and must not cross Statistical Local Area (SLA) boundaries and, as a consequence, any other ASGC spatial unit boundary.
- CDs in aggregate must cover the whole of Australia without gaps or overlaps.
CDs are created in response to significant changes in population within a given area, or if boundaries of larger geographic areas change. For example:
- If the population within an existing CD increases to the point of being too large for one collector, the CD may be split into two or more CDs.
- If growth in the population of a locality or urban centre results in expansion of its boundary, new CDs may be created by division of the CDs into which the growth intrudes, so that the new boundary may adequately reflect the urban growth in Census results (this process is often referred to as fragmentation).
Where necessary, CDs are created or boundaries adjusted to conform with changes to LGA boundaries.
The aim of these procedures is to maintain as much comparability between Censuses as possible.
New CD boundaries are designed with reference to information obtained from:
- government authorities;
- Census collector comments from the previous Census;
- local knowledge;
- field inspections; and
- the PSMA Australia national topographic dataset.
There are many types of Collection Districts including:
Off-Shore CDs: These CDs contain people who are enumerated on off-shore oil rigs, drilling platforms and the like. There is one Off-Shore CD for each state and the Northern Territory. Census data from respondents who completed their Census forms in the Australian Antarctic Territory are coded to an additional Off-Shore CD in Tasmania;
Shipping CDs: These CDs cover an area of water, normally a port, which is controlled by a Port Authority.
Shipping CDs contain people who are enumerated aboard ship in Australian waters. This includes commercial cargo vessels, passenger liners, ocean going passenger/car ferries, and dredges. People enumerated on board commercial vessels between Australian ports are also attributed to Shipping CDs. Foreign crews on ships are excluded from Census enumeration;
Migratory CDs: contain people who are enumerated on an overnight journey by train or bus. There is one Migratory CD for each state and the Northern Territory;
Water CDs: These CDs are assigned to bodies of water only that are required to be separated from the land area for enumeration and dissemination purposes. For example, sections of Sydney Harbour where people are likely to be resident on vessels on Census Night.
Water CDs have a default land-based CD so that any person enumerated in a water CD is coded to the default land-based CD. This ensures people are not mapped in waterways. Water CDs therefore do not have any statistical data associated with them, and are nil CDs.
See also Australian Standard Geographical Classification (ASGC).
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