Area unit population projections provide an indication of likely changes in the future size and age-sex structure of the population usually living in each area unit. You can use this information to see how particular areas will change in the future.
Area units are roughly the size of suburbs, but the 1,927 area units (boundaries at 30 June 2009) cover all of New Zealand and can be aggregated to meet your needs. The median size of area units is 2,000 people, while three-quarters of area units have a population between 100 and 4,000.
Users of projections range from planners to policy analysts, researchers to marketers. Government sector and community organisations use the projections to assess future needs for facilities and services such as housing, transport, schools, and recreation. Businesses can use the projections to analyse the potential market for new products and services, to site the location of new stores, and to develop strategic marketing initiatives.
More information
The updated 2006-base area unit population projections, including projections by five-year age group and sex, are available from Table Builder. These supersede the original 2006-base area unit population projections. The original 2006-base population projections will continue to be available on Table Builder until all 2006-base projections (eg subnational, ethnic population, family and household, labour force) have been updated.
Special projections can be produced for clients using their own assumptions. For more information and quotes, email demography@stats.govt.nz or telephone 0508 525 525 toll free.
In addition to area unit population projections, National Population Projections and Subnational Population Projections (for regions, cities and districts) are available from our website.
What is the base population?
The new area unit population projections have as a base the estimated resident population of each area at 30 June 2006. This population (4.185 million) was based on the census usually resident population count (4.028 million) of each area at 7 March 2006 with adjustments for: net census undercount
- net census undercount (+80,000)
- residents temporarily overseas on census night (+64,000)
- births, deaths, and net migration between census night (7 March 2006) and 30 June 2006 (+9,000)
- reconciliation with demographic estimates at ages 0–4 years (+3,000).
The estimated and projected resident population is not directly comparable with the census usually resident population count because of these adjustments. For more information about the base population, refer to Information about the Population Estimates.
Alternative series are available
Three alternative series (designated low, medium, and high) have been produced for each area unit using different fertility, mortality, and migration assumptions. Users can make their own judgement as to which projection series is/are most suitable for their purposes. However, at the time of release, Statistics NZ considers the medium projection series the most suitable for assessing future population changes. The medium series is consistent with mid-range series 5 of the National Population Projections: 2009(base)–2061 (released on 27 October 2009) and the medium series of the Subnational Population Projections: 2006(base)–2031 update (released on 24 February 2010).
The low and high projection series allow users to assess the impact on population size and structure resulting from more conservative and optimistic demographic scenarios, respectively. They are independent of any series of the national population projections or subnational population projections (regions, cities, and districts) as they represent plausible alternative scenarios for each area unit. As a result, low and high population projections at the area unit level do not necessarily sum to low and high population projections at broader geographic levels. The low projection series uses low fertility, high mortality, and low net migration for each area unit. The high projection series uses high fertility, low mortality, and high net migration for each area unit.
Nature of projections
Demographic projections are designed to meet both short-term and long-term planning needs, but are not designed to be exact forecasts or to project specific annual variation. The area unit population projections are based on assumptions made about future fertility, mortality, and migration patterns of the population. Although the assumptions are carefully formulated to represent future trends, they are subject to uncertainty. Therefore, the projections should be used as guidelines and an indication of the overall trend, rather than as exact forecasts.
While the projections take account of land planning and other government decisions known at the time the projections were made, Statistics NZ does not always have access to the policies or decisions of local and central government and businesses that assist in accurately forecasting small area populations. The projections do not take into account non-demographic factors (eg war, catastrophes, or major government and business decisions) which may affect future demographic behaviour. The unpredictability of migration trends, especially in the short-term, can have a significant effect on projection results.
It is important to recognise that the projections simply reflect the assumptions made about future fertility, mortality, and migration trends. While the assumptions are formulated from assessing short-term and long-term demographic trends, there is no certainty that any of the assumptions will be realised.
Method and assumptions
The cohort component method has been used to derive the population projections. In this method, the base population is projected forward by calculating the effect of deaths and migration within each age-sex group according to specified mortality and migration assumptions. New birth cohorts are generated by applying specified fertility assumptions to the female population of childbearing age.
Projection assumptions are formulated after analysis of short-term and long-term historical trends, government policy, information provided by local planners (eg housing subdivisions, zoning changes, commencement/expansion/closure of industries) and other relevant information. The projections incorporate the latest demographic information available at the time of production, including birth and death registrations to June 2009.
The assumed fertility and mortality rates are based on the registered births and deaths, respectively, for each area during the period 2007–09. The assumed rates are also consistent with the assumed rates for higher geographic levels (ie medium fertility and mortality variants for each territorial authority area and New Zealand).
Migration at the subnational level has both an internal migration (to/from other areas of New Zealand) and an external migration (to/from overseas) component, although these separate components are difficult to quantify because of insufficient data. The assumed net migration for each area is based on observed net migration during each five-year period from 1981 to 2006, the estimated net migration in the years ended June 2007–09, the capacity of the area for further growth (for areas with net inflow), whether historical outflows can be sustained (for areas with net outflow), the desirability of the area to new migrants, and information available from and about local authority areas that relates to current and future developments and may affect population change.
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