These maps show the percentage of each Territorial Authority Area’s (TA) population by broad age group, according to Statistics New Zealand’s High, Medium and Low Variant assumptions (Statistics New Zealand 2017, 2013(base)–2043 Update; data for key functional age groups are also given (such as the ratio of people at the main labour market entry ages to those approaching ‘exit’ age). The different indices illustrate the general progression of structural ageing (the general shift from lower to higher proportions at older ages and from higher to lower proportions at younger ages): at the older ages, the colours deepen over time, while at younger ages they lighten, but in each case do so differently for each TA. However, the generally progressive nature of the trends can also be confusing to interpret, as they are not strictly linear. The differences by variant also require some thinking about. For example, under the high variant assumptions there are lower proportions at older ages (and slower structural ageing), reflecting the greater impact of higher birth rates and higher migration at younger ages, while under the low variant assumptions, proportions at older ages are greater (and structural ageing is accelerated), reflecting the opposite (lower birth rates and migration at the younger ages). See for additional detail and important methodological notes