RESEARCH PAPER SERIES, 2019–20              Updated 28 APRIL 2021

Postal Area to Commonwealth Electoral Divisions

Christopher Giuliano

Statistics and Mapping

This Quick Guide explains how data available at postcode level can be converted to Commonwealth Electoral Divisions.

Postcodes are a four digit number used by Australia Post to assist with mail delivery. They form part of an address, which can potentially be used to produce administrative data (such as ATO data which based on taxpayers’ addresses). Postcodes however, have changeable, non-contiguous, complex boundaries, which makes them difficult to use for other purposes, such as analysing data at a state or sub-state level. The best publicly-available approximation of postcodes is Postal Areas (POAs), as defined by the Australian Bureau of Statistics (ABS). This Quick Guide assists researchers to go one step further by providing a correspondence of POAs to the Commonwealth Electoral Division (CED) boundaries in use at the 2019 election.

While postcodes cover most, but not all of Australia, POAs cover the whole nation; with eight crossing state boundaries. POAs can be used to report data for small geographic areas, or be aggregated to create larger regions, such as CEDs. This is where a correspondence is helpful. A correspondence is a file of spatial units (defined areas such as states, electorates, POAs and ABS-defined statistical areas) showing the proportion of each area’s (say) population that falls within another area—in this case, the proportion of the population of the POA that falls within a CED. This particular correspondence includes additional codes that are not POAs, i.e. Australia Post postcodes related to post office boxes or mail centres obtained from other sources such as Australian Tax Office (ATO) data. In such cases the physical location has been used to assign these additional codes to a CED.

The example on the second page shows the Division of Burt (blue area) with POAs overlayed. Clearly not all POAs fit neatly within Burt and this is when a correspondence is used to determine how much various POAs are allocated to Burt, based on very small area (SA1) population data. The map shows that 6108 is the only postal area contained wholly within Burt; all others are partially allocated to Burt in the correspondence, as indicated by the orange outlines.

An allocation is a simplified version of a correspondence, where whole areas are assigned to other areas based on (usually) where the majority of the population lives. In the Burt example, POA 6147 (shaded grey) also sits partially within Burt, but the majority of its population is outside Burt and it is therefore wholly allocated to another CED. Although a large area of 6111 appears to be outside of Burt, this is mostly farmland and therefore does not contain as much population as the area sitting within Burt. This area is therefore wholly assigned to Burt in the allocation, but only partially in the correspondence.

Map 1: Burt Commonwealth Electoral Division and Postal Areas

Contents of the correspondence file

This spreadsheet (download Excel spreadsheet here) contains four worksheets, which are summarised below.

·         Notes contains a more detailed explanation of the construction and limitations of the Correspondence and Allocation worksheets.

·         Correspondence provides each Postal Area (POA) and the name of the CED that it is in entirely, or, where the POA is in two or more electorates, the proportion of the POA population that is in each electorate. For example:

o        POA 2018 spans two electorates, with 56.87 per cent of the population in Kingsford-Smith and 43.13 per cent in Sydney.

o        POA 0872 spans four electorates across three jurisdictions—78.91 per cent of the population is in Lingiari (Northern Territory), 12.85 per cent is in Grey (South Australia), 6.64 per cent is in O’Connor and 1.60 per cent is in Durack (both in (Western Australia).

·         Allocation shows each POA against the CED that has the highest proportion of the POA’s population. Taking the POA 2018 example, it would only be listed for the electorate of Kingsford-Smith, as it has a higher proportion of the POA population than the electorate of Sydney. Just over 80 per cent of POAs have a population entirely within a CED.

·         Non-POA postcodes list postcodes that are not in the list of ABS POAs, such as post office boxes.

Further notes on use

The Postal Area (POA) correspondence is underpinned by Estimated Resident Population weighting and should not be used for data which does not correlate with population, or where the population may be unevenly distributed, such as infrastructure, agriculture, or business-level data. For more information see ABS, Australian Statistical Geography Standard (ASGS) Correspondences.

This correspondence and allocation is provided in good faith and represents the best efforts of the Parliamentary Library to provide an association of POAs to CEDs. This dataset should be considered indicative only, and the choice to use it rests with the user. This correspondence/allocation may not match those produced by the ABS or other parties due to differences in methodology. The Parliamentary Library may update this dataset when new small area population data is released, or when there is a redistribution of electoral boundaries.

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