*2.2. Unit of Analysis*

An appropriate unit of analysis is critical in geography-based analyses. Every five years, ABS counts every person and home in Australia, in the Census of Population and Housing. For the 2011 and 2016 Census, Statistical Area Level 1 (SA1) was designed for a detailed spatial analysis of the Census data. This research used these areas to examine how Census characteristics vary at a neighbourhood scale within larger areas [23]. For the 2006 Census, the Census Collection District (CD) was designed as the smallest unit for data collection and processing—including about 200 dwellings. CD was the basis of output for most data and served as the basic building block in the Australian Standard Geographical Classification (ASGC) [24].

It should be noted that although CD in 2006 and SA1 in 2011 and 2016 were the basic census units of the same level for the data analysis in this study, the number of census units for SA1 were higher than that of CD because of the increase of population and immigrants. Nevertheless, as the purpose of this study is to understand the formation trend of NORCs over time, which focused on the population changes and the distribution features of the older population (65+), the slight differences in the number and scale between SA1 and CD units do not affect the overall result.
