Development of census output areas with AZTool in South Africa

Abstract

The use of a single geographical unit to both collect and disseminate census data is common in many countries across the world, especially in developing countries. In South Africa this approach poses some challenges, as the design of small geographical units called enumeration areas to facilitate data collection differs considerably from the design of units that aid data analysis and interpretation. We aimed to create optimised census output areas using the Automated Zone-design Tool (AZTool) program, using the 2001 census enumeration areas as building blocks at various spatial levels, for both rural and urban settings in two South African provinces. The results were consistent and stable. The primary criterion of the confidentiality limit of 500 people was respected at all geographical levels or regions, in both urban and rural settings, for newly created optimised output areas. For the second criterion, lower intra-area correlation values at lower geographical levels for both rural and urban areas showed that higher geographical levels produced more homogeneous output areas than did lower geographical levels or regions. Our obtained intra-area correlation of 0.62 for the two provinces combined indicated that the selected homogeneity variables were good indicators of social homogeneity for creating optimised output areas in South Africa. We conclude that the AZTool software can be used to effectively and objectively create optimised output areas for South African data. Further research on the comparison of the newly created output areas with existing output areas in South Africa should be explored.

Effects of different building blocks designs on the statistical characteristics of Automated Zone-design Tool output areas

“…Two provinces were selected for this study; Free State and Gauteng, which were representatives of rural and urban areas, respectively (Mokhele et al, 2016). In each province, different spatial or geography levels such as district, municipality and mainplace were selected for subsequent analysis.…”

“…The Automated Zone-design Tool program algorithms usually take input building blocks and iteratively aggregate them into larger output areas from an initial random aggregation, by checking the effect of swapping individual building blocks between output areas based on criteria set by the user (Openshaw, 1977;Mokhele et al, 2016). All the AZTool output areas were generated using different building blocks with a population threshold of 500 (as practised by Stats SA) and a population target of 1000 to ensure confidentiality limit (Verhoef and Grobbelaar, 2005;Mokhele et al, 2016). Confidentiality limit is minimum population that is used for the dissemination of census data in order to avoid personal information disclosure.…”

“…In South Africa, these small areas (such as EAs) normally contain from 100 to 250 households (Stats SA, 2003;Stats SA and HSRC, 2007;Verhoef and Grobbelaar, 2005). The criteria for the design of EAs are that: firstly, they should not overlap; secondly, they should be compact without pockets or disjointed sections and should cover the entire country; thirdly, they should have boundaries that could be identified on the ground; and last but not the least, they should be of approximately equal population size to enable an enumerator to cover each one in the allocated census period (Stats SA and HSRC, 2007;Mokhele et al, 2016). Before 1996, the boundaries for EAs were hand-drawn, which is traditional demarcation (Laldaparsad, 2007).…”

“…A new spatial layer, the SAL, was therefore created using the non-zone design approach in 2005 for release of the 2001 census data at lower level. A similar non-zone design approach was also employed in the creation of SAL for the 2011 census data (Mokhele et al, 2016).…”

“…This results in a problem called the Modifiable Areal Unit Problem (MAUP) originally discovered by Gehlke and Biehl (1934). The 2007; Dumedah et al, 2008;Ralphs and Ang, 2009;Flowerdew, 2011;Mokhele et al, 2016).…”