• Summary
• Downloads
• Explanatory Notes
• Related Information
• Past Releases

A postcode is a four digit number used by Australia Post to assist with mail delivery. As it is readily available on the end of each postal address, many researchers and businesses use postcode as a make-shift geographic region for aggregation and analysis of address based data. The desire to compare such data to census data in turn creates demand for census data aggregated by postcode. Census data are collected on Collection Districts (CDs) which, for several reasons, are not compatible with postcodes. The Australian Bureau of Statistics (ABS) has, however developed a Census Geographic Area classification known as Postal Areas which approximates the area of those postcodes where people live.

Postal Area

Postal Areas are created by allocating whole CDs to Australia Post postcode areas on a 'best fit' basis (See Statistical Geography: Volume 2 - Census Geographic Areas (Cat. no. 2905.0) available July 2007). Postal Areas derived in this way only approximate Australia Post postcode boundaries.

In developing Postal Areas each CD is allocated an Australia Post postcode. Allocations are made based on the distribution of addresses and not area. This means that a CD is allocated to a postcode if the majority of the residential address points¹ in that CD are contained within that postcode. Postal Areas are then formed by joining together the CDs that have been allocated the same postcode.

Allocations have been determined using the best available information on postcode boundaries. Unfortunately official maps of postcode boundaries have not been updated since the early 1990s and none of the more recent interpretations have been endorsed by Australia Post. Users should, therefore, be aware of the limitations of the Postal Area classification.

Some Australia Post postcodes are not included in the Postal Area classification. For instance, in some cases when applying the 'best fit' principle there is no CD which can be allocated to a particular Australia Post postcode. This occurs in two cases:

• where a CD covers two or more whole postcodes, the CD can be allocated to only one Postal Area; or
• where more than one CD partially covers a postcode but all the CDs are allocated to other postcodes with which they also share area.

Postal Areas that cross State/Territory borders:

Where Postal Areas cross State/Territory borders standard census products will provide data for the entire Postal Area.

2. Digital boundaries

Postal Area digital boundaries are Census Geographic boundaries and are available as part of the 2006 Census DataPacks (Cat No. 2069.0.30.001 to 2069.0.30.007), Australia CD-ROM. More information on Census Geographic boundaries can be found in Statistical Geography Volume 2 - Census Geographic Areas (Cat no. 2905.0).

Postal Area digital boundaries are supplied in both MapInfo Export (.mif/.mid) and ESRI Shape formats. These are suitable for import into geographic information systems and desktop mapping packages. All spatial data released by the ABS are published in unprojected geographic coordinates and after August 2001 are based on the Geocentric Datum of Australia,1994 (GDA94). For more information on GDA94 see the Fact Sheet Geocentric Datum of Australia and Australian Bureau of Statistics Boundaries.

3. Comparing other postcode based statistics to census statistics
Users of census data can have trouble reconciling their own postcode based statistics with census statistics because:

• Many respondents mis-report their postcode;
• It is also difficult to say what the 'correct' postcode for some respondents should be, especially when considering post office boxes and rural delivery services. Census data are based either upon the Postal Area of the residence where a person was enumerated or the Postal Area where they normally reside. By contrast many non-ABS datasets only record the postcode of a person's mailing address. Since many people have different mailing and residential addresses the datasets are difficult to reconcile; and
• postcode boundaries change over time and it can take a long time for respondents and coding systems to adjust to a change in a postcode. This causes problems when working with postcode based data taken from different reference periods as the changes to the boundaries are difficult to reconcile with changes in the population.
  

The primary consideration when doing a comparison with census data based on the Postal Area classification is that the Postal Areas are derived using a 'best fit' of whole CDs. The census data are correct for the Postal Area but the Postal Area only approximates the area of the postcode. The Postal Area classification also excludes some postcodes and as such there will be no census data for these postcodes.

Postal Area of Usual Address Census Night (POCUCP)

Postal Area of Usual Address Census Night (POCUCP) is a census variable which identifies the Postal Area of the person's usual address. For people counted at home, the value for POCUCP is determined from the CD of the residence. For people enumerated away from home, their usual address is coded to a CD where possible and then the Postal Area of that CD is used. Where a person does not state his/her place of usual residence they are coded to Postal Area undefined. For example:

4. Alternatives to postcode/postal area census data

2006 Census data is available by CD of usual residence. Users of census data who previously resorted to Postal Area data may instead wish to consider using CD of usual residence.

2006 Census State Suburbs (See Statistical Geography: Volume 2 - Census Geographic Areas (Cat. no. 2905.0)) have been defined for most of Australia. Many users of Postal Area data may find that the suburb is a more convenient and more readily recognisable geographical area for their purposes. In many cities there is a many-to-one relationship between suburb and postcode so in theses cases suburb data also provide a finer level of geographical resolution.

5. Unallocated Australia Post Postcodes

Some Australia Post postcodes are not included in the Postal Area classification. For instance, in some cases when applying the 'best fit' principle there is no CD which can be allocated to a particular Australia Post postcode. This occurs in two cases:

• where a CD covers two or more whole postcodes, the CD can be allocated to only one Postal Area; or
• where more than one CD partially covers a postcode but all the CDs are allocated to other postcodes with which they also share area.

Listing of Unallocated Australia Post Postcodes

1. New South Wales

2. Victoria

3. Queensland

4. South Australia

5. Western Australia

6. Tasmania

7. Northern Territory

8. Australian Capital Territory

No unallocated Australia Post postcodes

9. Other Territory

No unallocated Australia Post postcodes

Notes

¹ Residential address points were derived from the Geocoded National Address File.