EXPLANATORY NOTES
INTRODUCTION
1 This product contains estimates of the resident population of Statistical Areas Level 2 to 4 (SA2s  SA4s) and Greater Capital City Statistical Areas (GCCSAs) of Australia. These estimates plus those for Local Government Areas (LGAs), Significant Urban Areas (SUAs), Remoteness Areas (RAs) and Electoral Divisions are also provided in the Downloads tab of this issue.
2 To meet the conflicting demands for accuracy and timeliness, there are several versions of substate/territory population estimates. Preliminary estimates as at 30 June are normally available by April of the following year, revised estimates twelve months later and rebased and final estimates after the following Census. The estimates in this issue are final for 2003 to 2011, revised for 2012, and preliminary for 2013.
ESTIMATED RESIDENT POPULATION  AUSTRALIA
3 Estimated resident population (ERP) is the official estimate of the Australian population, which links people to a place of usual residence within Australia. Usual residence within Australia refers to that address at which the person has lived or intends to live for six months or more in a given reference year.
4 Estimates of the resident population are based on Census counts by place of usual residence (excluding shortterm overseas visitors in Australia), with an allowance for Census net undercount, to which are added the estimated number of Australian residents temporarily overseas at the time of the Census.
5 Population estimates for Australia and the states and territories are updated by adding to the estimated population at the beginning of each period the components of natural increase (births minus deaths, on a usual residence basis) and net overseas migration. For the states and territories, account is also taken of estimated interstate movements involving a change of usual residence. After each Census, estimates for the preceding intercensal period are finalised (rebased) by incorporating an additional adjustment (intercensal error or intercensal difference) to ensure that the difference between the ERPs at the two respective Census dates agrees with the total intercensal change.
6 Throughout 2013, the ABS conducted a oneoff exercise to revise (recast) population estimates for a longer time period, back to 1991. This was necessary due to a significant improvement in the methodology used to estimate net undercount in the 2011 Census. For more information, refer to the 20 June 2013 release of Australian Demographic Statistics, Feature Article 2: Recasting 20 years of ERP.
7 More detailed explanations of the concept of ERP, as adopted by the ABS for official population estimates, are contained in Information Paper: Population Concepts, 2008 (cat. no. 3107.0.55.006) and Population Estimates: Concepts, Sources and Methods, 2009 (cat. no. 3228.0.55.001).
ESTIMATION OF SUBSTATE POPULATIONS
8 In Australia, the SA2 (as defined in the Australian Statistical Geography Standard (ASGS)) is the base spatial unit used to collect and disseminate statistics other than those collected from the Population Census. In aggregate, SA2s cover the whole of Australia without gaps or overlaps. Populations for SA2s are estimated as at 30 June each year. Population estimates for larger regions are built up from SA2level estimates.
9 The ERP as at Census date for each SA2 is calculated based on usual residence Census counts, excluding shortterm overseas visitors in Australia, with an allowance for Census net undercount and the number of residents temporarily overseas (RTOs) at the Census date. The estimates of net undercount are apportioned to SA2s based on age, sex, Indigenous status, state and territory, and broad region. The number of RTOs on Census night is estimated based on coding addresses of residence to SA2 from a sample of incoming passenger cards provided to the Department of Immigration and Border Protection. As the Census is not held on 30 June (the 2011 Census was held on 9 August), further adjustments taking into account births, deaths and migration for the intervening period are made to obtain the ERP at 30 June. A procedure is then applied to avoid the release of unconfidentialised usual residence Census counts while maintaining closeness to the unconfidentialised ERP.
10 For postCensus years, the absence of migration data at the SA2 level means that it is not possible to estimate SA2 populations by taking into account natural increase and net migration. Instead, ERP for most SA2s is calculated using a mathematical model, where relationships are established between changes in population and changes in indicator data between the two most recent Censuses for groups of SA2s. Current indicators include dwelling approvals, Medicare enrolments and counts of people on the Australian Electoral Roll. Changes in these indicators are used to estimate changes in the population of each area since the last Census. In areas where indicator data is unreliable or migration can be assumed to be insignificant, population change may be estimated by adding natural increase (births minus deaths) since the previous Census. In some very small areas population change since the previous Census may be assumed to be zero in the absence of reliable indicator data for these areas. All estimates are scrutinised and validated by ABS analysts. Local knowledge, including that advised by local governments, may be used to adjust the figures for particular SA2s. Estimates at the SA2 level are constrained so that they add to the relevant state/territory population estimates.
11 The 2012 estimates in this issue supersede those released in previous issues of this product. In addition to the normal annual update to preliminary substate population estimates (to take into account revisions to preliminary state and territory estimates), the revised 2012 series uses new estimation models. The new models use the improved historical population series and final rebased 2011 estimates (refer to paragraph 6) to establish stronger relationships between population and indicator data. The improved models will be used to estimate substate populations out to 2016. The 2012 estimates will not change again until they are finalised after the 2016 Census.
12 To enable the comparison of regional populations over time, historical population estimates based on consistent updated geographic boundaries are prepared. These estimates correspond with previously released estimates (on different boundaries) where possible. When official statistical boundaries, such as Local Government Areas, are updated, historical estimates are prepared based on the updated boundaries.
13 In Census years, both preliminary estimates (derived from updating ERP from the previous Census) and rebased estimates (based on the current Census) are prepared. Differences between these two sets of estimates are referred to as intercensal errors/intercensal differences. Rebased estimates of SA2 populations for previous intercensal years are based on estimates derived by apportioning the intercensal error/intercensal difference evenly across the five years, while constraining the SA2 level estimates so that they sum to state/territory estimates. Rebased 2007 to 2010 estimates were derived by adding onefifth of the 2011 intercensal error/intercensal difference to the previous estimate of the 2007 population, twofifths to the previous estimate of the 2008 population, and so on.
ACCURACY OF SUBSTATE POPULATION ESTIMATES
14 An indication of the accuracy of ERPs can be gauged by assessing the size and direction of the intercensal errors/intercensal differences. For Australia, the preliminary (unrebased) June 2011 ERP overestimated the final rebased June 2011 ERP by 1.2% (278,300 people). For the states and territories, the 2011 intercensal errors/intercensal differences ranged from 0.6% (Australian Capital Territory) to +2.3% (Queensland).
15 Summary statistics of the absolute values of these errors or differences can be used to assess the accuracy of a number of population estimates. To give an indication of the quality of SA2based estimates, a set of experimental unrebased 2011 estimates was prepared, updated from 2006 Censusbased estimates and constrained so that they summed to final rebased state/territory ERP. These were compared with the final rebased 2011 SA2 estimates. The average absolute value of the intercensal errors/intercensal differences for this series of 2011 SA2 estimates (excluding areas with less than 1,000 people) was 3.5%.
16 Average absolute intercensal errors/intercensal differences for the 2011 SA2 experimental estimates decreased with increasing population size; that is, SA2s with large populations recorded the smallest percentage errors while small SA2s had the largest percentage errors.
Average absolute intercensal error/intercensal difference, Australia  30 June 2011 

 Number of SA2s  Average absolute intercensal error/intercensal difference 
Size of SA2 (people)  no.  % 

1,000 to 3,000  99  5.9 
3,000 to 4,999  335  4.3 
5,000 to 6,999  327  3.9 
7,000 to 9,999  383  3.5 
10,000 to 14,999  414  3.2 
15,000 to 19,999  292  2.7 
20,000 and over  224  2.3 

17 In recognition of the inherent inaccuracy involved in estimating population, population figures in text and accompanying summary tables published by the ABS are generally rounded. In the commentary for this product, figures less than 1,000 are rounded to the nearest ten, figures over 1,000 are rounded to the nearest hundred, and figures over 1 million are rounded to the nearest 10,000 or 100,000. While unrounded figures are provided in the spreadsheets, accuracy to the last digit should not be assumed. Estimates of change in population are based on unrounded numbers.
SA1BASED POPULATIONS
18 The Statistical Area Level 1 (SA1) is the smallest geographic unit for the release of Census data. There are approximately 55,000 SA1s and they cover the whole of Australia without gaps or overlaps. To provide some indication of estimated resident population below the SA2 level, the ABS prepares population estimates for SA1s. These estimates can be aggregated to form population estimates for regions such as State Suburbs, Remoteness Areas and Electoral Divisions. By this means, population estimates for areas other than those provided in this product (including SA1 ERPs) may be available on request.
19 Population estimates at the SA1 level as at 30 June of a Census year are compiled by apportioning the population estimate for each SA2 across the SA1s within the SA2, using Census usual residence counts. In postCensus years, the 30 June population estimates for SA2s are apportioned across SA1s by taking into account population change implied by indicator data at the SA1level in the years following the Census.
LOCAL GOVERNMENT AREA POPULATIONS
20 Population estimates for LGAs that can be built from whole SA2s are produced by aggregating the SA2level estimates accordingly. Estimates for LGAs that can be built from whole SA1s are produced by aggregating the SA1level estimates. In Census years, where LGAs cross SA1 boundaries, mesh block Census counts are used to estimate the share of the SA1 population that reside in those LGAs. In post Census years, estimates are prepared using updated estimates of SA1 to LGAs splits, taking into account population change implied by indicator data. Whole and partial SA1 estimates are then aggregated to LGA level.
AUSTRALIAN STATISTICAL AREAS
21 This publication contains data presented according to the 2011 edition of the Australian Statistical Geography Standard (ASGS), which refers to boundaries as defined at 1 July 2011. Under this classification, statistical areas are defined as follows:
 Statistical Areas Level 2 (SA2s). SA2s are mediumsized general purpose areas which aim to represent communities that interact together socially and economically. SA2s are based on officially gazetted suburbs and localities. In urban areas SA2s largely conform to one or more whole suburbs, while in rural areas they generally define the functional zone of a regional centre.
 Statistical Areas Level 3 (SA3s). SA3s are aggregations of whole SA2s and reflect a combination of widely recognised informal regions as well as administrative regions such as state government regions in rural areas and Local Government Areas in urban areas.
 Statistical Areas Level 4 (SA4s). SA4s are made up of whole SA3s and are designed to reflect labour markets. In rural areas, SA4s generally represent aggregations of small labour markets with socioeconomic connections or similar industry characteristics. Large regional city labour markets are generally defined by a single SA4. Within major metropolitan labour markets SA4s represent sublabour markets.
 Greater Capital City Statistical Areas (GCCSAs). GCCSAs are built from whole SA4s and represent a broad socioeconomic definition of each of the eight state and territory capital cities. They contain not only the urban area of the city, but also the surrounding and nonurban areas where much of the population has strong links to the capital city, through for example, commuting to work.
 Remoteness Areas (RAs). RAs represent an aggregation of noncontiguous geographical areas which share common characteristics of remoteness. The delimitation criteria for RAs are based on the Accessibility/Remoteness Index of Australia (ARIA+), which measures the remoteness of a point based on the road distance to the nearest urban centre. The RA categories range from Major Cities to Very Remote. Each RA is created from a grouping of SA1s which have a particular degree of remoteness.
 Significant Urban Areas (SUAs). SUAs are aggregations of whole SA2s which represent concentrations of urban development with populations of 10,000 people or more. They do not necessarily represent a single Urban Centre, as they can represent a cluster of related Urban Centres with a core urban population over 10,000 people. They can also include related periurban and satellite development and the area into which the urban development is likely to expand. SUAs may cross a state or territory border.
 State Electoral Divisions (SEDs). An SED is an area legally prescribed for returning one or more members to the State or Territory Lower Houses of Parliament. Data for SEDs are approximated by aggregating the data for Statistical Areas Level 1 that best fit the area.
22 This product also contains data presented according to the 2013 edition of the Australian Statistical Geography Standard (ASGS)  Non ABS Structures.
 Local Government Areas (LGAs). LGAs are ABS approximations of officially gazetted LGAs as defined by each state and territory local government department. LGAs cover incorporated areas of Australia, which are legally designated areas for which incorporated local governing bodies have responsibility. The ABS updates LGAs annually, and prepares updated and historical population estimates based on these updated boundaries.
 Commonwealth Electoral Divisions (CEDs). A CED is an area legally prescribed for returning one member to the House of Representatives, Australia's Federal Lower House of Parliament. Data for CEDs are approximated by aggregating the data for Statistical Areas Level 1 that best fit the area.
23 Further information on these statistical areas is contained in:
24 A complete series of SA2 maps is available in
Australian Statistical Geography Standard: Volume 1  Main Structure and Greater Capital City Statistical Areas, July 2011 (cat. no. 1270.0.55.001).
RANKING POPULATION CHANGE
25 This product ranks regions according to both 'largest' and 'fastest' growth, identifying areas with significant changes in population. Largest growth is based on the absolute change in population between June 2012 and June 2013, while fastest growth is based on the rate of change in population (expressed as a percentage). Regions with populations of less than 1,000 people at June 2012 have been excluded from the fastest growth rankings.
26 Due to the inherent imprecision of regional population estimates and variation in population size, rankings should be considered indicative of relative growth between regions, not definitive.
CENTRE OF POPULATION
27 The centre of population is a measure used to describe the spatial distribution of a population. The method used to calculate centres of population in this product is based on the centroid and population of each Statistical Area Level 1 (SA1). To calculate the centre of population for an area, the latitude and longitude coordinates of the centroid of each SA1 in that area are multiplied by the SA1's estimated resident population to obtain weighted latitudes and longitudes for each SA1. These are summed to obtain a weighted latitude and longitude coordinate for the area, then divided by the total population of the area to obtain a single latitude and longitude coordinate.
28 Due to the inherent imprecision in small area estimates, the centre of population should be considered indicative only of the distribution of population, and cannot be ascribed to an exact location. The use of different geographical level data can result in different centres of population.
CALCULATION OF AREAS AND POPULATION DENSITY
29 The area figures used in this issue are based upon the SA2 level of the 2011 edition of the ASGS. The areas of the SA2s were calculated using ABS standard Geographic Information Systems software from the digital boundaries of this ASGS edition. Higher level spatial unit area figures are aggregations of the relevant SA2 areas. These areas are included in the SA2based spreadsheet accompanying this publication.
30 The population density for an area is calculated by dividing its estimated resident population by its area in square kilometres. The result is expressed as a number of people per square kilometre. The population densities of SA2s are illustrated in the Population Density maps in this product. These maps should be considered an approximation of the true distribution of the population. For example, an SA2 comprising one or more small population centres surrounded by a large, sparsely populated area will be illustrated with the average population density for the SA2 as a whole, so the small population centres will not be apparent.
ACKNOWLEDGMENT
31 ABS publications draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the
Census and Statistics Act 1905.
RELATED RELEASES
32 Other ABS releases that are freely available on the ABS website <
www.abs.gov.au> and may be of interest to users of this product include:
ADDITIONAL STATISTICS AVAILABLE
33 As well as the statistics included in this and related publications, additional information is available from the
Demography Topics @ a Glance page on the ABS website <
www.abs.gov.au>.
34 The ABS may have other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070. The
ABS Privacy Policy outlines how the ABS will handle any personal information that you provide to us.
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