Medium projection: Assuming medium fertility, medium mortality, and medium net migration.
High projection: Assuming high fertility, low mortality, and high net migration.
Low projection: Assuming low fertility, high mortality, and low net migration.
Natural increase: live births minus deaths
Net migration: Long-term arrivals to the area minus long-term departures from the area. This includes migration within New Zealand
These projections have as a base the estimated resident population of each area at 30 June 2018. This population was based on the census usually resident population count of each area at 6 March 2018 and adjusted for:
a. net census undercount
b. residents temporarily overseas on census night
c. births, deaths, and net migration between census night (6 March 2018) and 30 June 2018
d. reconciliation with demographic estimates at ages 0–14 years.
The estimated and projected resident population is not directly comparable with the census usually resident population because of these adjustments.
Three alternative projections (designated low, medium, and high) have been produced for each area using different fertility, mortality, and migration assumptions. At the time of release, the medium projection is considered the most suitable for assessing future population change.
The low and high projections allow users to assess the impact on population size and structure resulting from lower growth and higher growth scenarios, respectively. The low projection uses low fertility, high mortality, and low net migration for each area. The high projection uses high fertility, low mortality, and high net migration for each area. The low and high projections are independent of the national population projections as they represent plausible alternative scenarios for each area.