Address coding, a form of geocoding, is a process where a unit record is assigned to a latitude/longitude point on the ground, or "coded" to a small area, such as a Mesh Block, by using the address. Once this has been established, the unit record can then be assigned to a larger geographic area. The data can then be added to other unit records that are assigned to the same area, thus providing aggregate values for the new geographic area.
If latitudes and longitudes are available, then it is possible to code these units to any level of the ASGS. This is the most accurate method for the transition of existing data. This removes the need to apply a mathematical transformation, as data coded to a point can be aggregated accurately to any area, regardless of its geographic base. The overall effect is an accurate recoding of the original data.
If a complete street address is available - that is street number and name, Suburb or Locality, State or Territory (S/T) and postcode - it is also possible to code the units to any level of the ASGS using address coding software. However, if some unit records do not contain complete addresses, such as missing street numbers, misspelt street names or incorrect Suburb or Locality names, then achieving an accurate match to a point on the ground may not be possible. As a result accurate coding to the smaller levels of the ASGS, such as Mesh Block or SA1, may not be achieved. It should be noted though, that incomplete or inaccurate addresses may still code accurately to the higher levels of the ASGS such as SA2 and above. Other addresses that can prove problematic include lot numbers and Rural Mail Box and Post Office Box addresses. In these cases manual data repair may be required to achieve the desired results.
Rural addressing is not consistent across Australia, though this is in the process of being standardised, and as a result a collection unit address may not achieve a match that will enable coding to the smaller levels of the ASGS.
When considering converting data to the ASGS, address coding and geocoding are considered to be the most accurate method of converting data and these options should be explored prior to using any of the other options discussed in this paper.
At present the ABS does not provide an address geocoding service, as we do not own the intellectual property of the Geocoded National Address File (G-NAF) file which is owned by PSMA Australia. The ABS does however have an agreement with PSMA Australia to include our Mesh Block codes in the G-NAF file. This allows G-NAF users to relate addresses to the ABS geography.
There are several commercial organisations that offer geocoding services, based on G-NAF. More details on these companies can be found on the PSMA Australia website: http://www.psma.com.au/data-access