Statistical Area Level 2 (SA2s) are functional areas that represent a community that interacts together socially and economically. They often align with Suburb and Locality boundaries to improve the geographic coding of data to these areas. In major urban areas SA2s often reflect one or more related suburbs. The SA2 is the smallest area for the release of many ABS statistics, including the Estimated Resident Population (ERP), Health & Vitals and Building Approvals data. SA2s generally have a population range of 3,000 to 25,000 persons, and have an average population of about 10,000 persons. 　

SA2s are aggregated from whole Statistical Areas Level 1 (SA1s) in the ASGS Main Structure. Whole SA2s aggregate to form Statistical Areas Level 3 (SA3s), Significant Urban Areas (SUAs) and Tourism Regions (TRs). 　

SA2s are contiguous and, in aggregate, cover the whole of Australia without gaps or overlaps.

More information can be found at

http://www.abs.gov.au/ausstats/abs@.nsf/mf/1270.0.55.001