The Statistical Area Level 1 (SA1) is the second smallest geographic area defined in the Australian Statistical Geography Standard (ASGS), the smallest being the Mesh Block. The SA1 has been designed for use in the Census of Population and Housing as the smallest unit for the processing and release of Census data. For the 2011 Census, SA1s will also be the basis of output for most data, the exception being some Place of Work destination zones. For 2011, SA1s also serve as the basic building block in the ASGS and are used for the aggregation of statistics to larger Census geographic areas.
An SA1 is represented by a unique seven digit code.
SA1s are designed to remain relatively constant over several Censuses. Future change will largely be dealt with by splitting existing SA1s. For the 2011 Census, there are approximately 54,000 SA1s throughout Australia (this includes the other territories of Christmas and Cocos (Keeling) Islands and Jervis Bay). SA1s cover the whole of Australia with no gaps or overlaps.
- Zero population SA1s are created in areas that are expected to have little or no permanently residing populations. Data from these areas are reassigned to a populated alternate SA1.
- Shipping SA1s 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 SA1s. Foreign crews on ships are excluded from Census enumeration. There is one Shipping SA1 for each state, the Northern Territory and Other Territories.
- Off-Shore SA1s contain people who are enumerated on off-shore oil rigs, drilling platforms and the like. There is one Off-Shore SA1 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 SA1 in Tasmania.
- Migratory SA1s contain people who are enumerated on an overnight journey by train or bus. There is one Migratory SA1 for each state, the Northern Territory and the Australian Capital Territory.