Working towards optimal dissemination geographies for Census 2011

1. Working towards optimal dissemination geographies for Census 2011 Ms H Verhoef Isibalo Symposium, Free State October 11, 2013

2. Introduction • Literature study • Needs assessment • Evaluation of 2001 output geographies • Recommendations and specifications for the 2011 small area design

3. Why does geography matter? Geography: • Where? • Spatial relationships and distribution • Visualisation

4. Nested hierarchy for the South African census of 2011

5. Census geography • Enumeration Areas – Collection geography • Designed to manage fieldwork • Homogeneity according to residential type or land use – EA type

6. Census data • Aggregated on different geographic levels • Generalisation • Loss of detail • Modifiable Areal Unit Problem

7. MAUP illustrated Source: www.zonedesignsystems.com/intro4 The Modifiable Areal Unit Problem/Zone Design Systems.

8. Enumeration Area Population Range

9. Output geography • What are other countries doing? • Problem with 2001 output geography • Very large physical areas • Island EAs/SAs

10. The problem with SA’s current output geography

11. Outcome of SAs’ user needs

12. Two options for input in the creation of small areas for 2011 • EAs: Inherit EA demarcation specifications and problems • Geo-coded record data: Not all 2011 records were geo code-able to addresses or smallest land parcels Create building blocks such used in the UK or Canada ?

13. Options for the output geography design • Same specifications as 2001 SAL - Same problems • Same specifications as 2001, except change population minimum from 500 to 300 - Potentially better (but still island problems) • Change specifications: - Find ideal tot pop within confidentiality frame - Test for the most wanted variables

14. Options for the output geography design (continue) • Re-demarcate the vacant areas to eliminate all island EAs and limit physical size when merging EAs - potentially better shapes and area size • Exclude vacant and populated areas with population below 10 - potentially better shapes and areas size NB: This option will result in non-contiguous coverage – suppressed areas blank

15. Census 2011 Small Areas As many as possible SAs = one EA, depending on the EA population size and acceptable level of confidentiality. The small areas should ideally be: • as small as possible in terms of physical area and population size, • as compact in shape as possible, • as homogeneous as possible (EA type), • fall within administrative boundaries.

16. South African hierarchies

17. Future research & development • Creation of new building blocks Blocks or block-faces similar to what is done in Canada or the postman walks in the UK • Useful to create all other areas such as wards, voting districts, policing areas etc. • Sample frames • Complete the address frame • Enable us to link census questionnaires to localities in stead of EAs • Create unique user determined output

18. Census data, publications and spatial files info@statssa.gov.za www.statssa.gov.za EA / PN & SA Spatial/geographic enquiries & comments helenev@statssa.gov.za