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RSS meeting: Nov 2000 PowerPoint Presentation
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RSS meeting: Nov 2000

RSS meeting: Nov 2000

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RSS meeting: Nov 2000

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  1. 2001 output areas: specification, demonstration and maintenance David Martin, Abigail Nolan, Mark Tranmer RSS meeting: Nov 2000

  2. Overview • 2001 Output areas • Specification • Demonstration • Maintenance • Current developments RSS meeting: Nov 2000

  3. 2001 Output areas • 1991: EDs designed for data collection, but used for both data collection and output • 2001: separation of collection and output geographies - purpose-specific geographies • New output areas built from synthetic unit postcode polygons • Application of automated zone design (after Openshaw, 1977) RSS meeting: Nov 2000

  4. OA design (1) Initial random aggregation of postcodes into potential output areas RSS meeting: Nov 2000

  5. OA design (2) Choose one postcode at random as candidate for swapping into a different output area RSS meeting: Nov 2000

  6. OA design (3) Make the swap and evaluate the impact on the overall solution RSS meeting: Nov 2000

  7. OA design (4) If swap does not result in improvement, go back to the previous configuration RSS meeting: Nov 2000

  8. OA design (5) Choose another postcode at random as candidate for swapping into another output area RSS meeting: Nov 2000

  9. OA design (6) If the swap results in an overall improvement, keep it as part of the solution, and examine a new potential swap... RSS meeting: Nov 2000

  10. Specification Initial Random Aggregation of Building Blocks Iterative Recombination Design Constraints (Contiguity, Thresholds, Shape, Size, Homogeneity) 2001 Output Areas RSS meeting: Nov 2000

  11. Constraints (1) • Contiguity: output areas from adjacent postcodes (NB problem of stacks) • Thresholds: output areas above population thresholds (NB problem of sub-threshold parishes) • Shape: output areas should be as compact as possible • minimize perimeter2/area RSS meeting: Nov 2000

  12. Constraints (2) • Size: output areas should be as uniformly sized as possible - avoiding very large and very small populations minimize S(OApop-target)2 • Homogeneity: output areas should be as socially uniform as possible • maximize intra-area correlations RSS meeting: Nov 2000

  13. Intra-area correlation • Measures similarity of values within any area of interest (Holt et al., 1996). Higher correlation = greater homogeneity (theoretical maximum of d = 1.0) • Can be computed for a single category (eg. owner occupied) or for multi-category variables • Tenure and dwelling type evaluated RSS meeting: Nov 2000

  14. Zone design experiments • ONS postcode polygons for test areas • Populated with plausible synthetic populations by iterative sampling of SAR individuals (PCs structured by dwel. type) • Test OAs constructed using alternative combinations of design constraints: (OApop only; OApop+shape; OApop+homog; OApop+shape+homog) RSS meeting: Nov 2000

  15. Illustrative results… RSS meeting: Nov 2000

  16. Illustrative results… RSS meeting: Nov 2000

  17. Illustrative results… RSS meeting: Nov 2000

  18. Illustrative results… RSS meeting: Nov 2000

  19. Demonstration: website http://www.geog.soton.ac.uk/research/oa2001/ RSS meeting: Nov 2000

  20. OA Demonstrator • Experimental results for Kerrier (rural-villages), Cardiff (urban-suburban) and Manchester (metropolitan) • ONS prototype postcode polygon set • Threshold population 100, targets of 150, 250 • Combinations of population, shape and intra-area correlation controls • PDF, CSV and Shape file samples online RSS meeting: Nov 2000

  21. Demonstrator data RSS meeting: Nov 2000

  22. Maintenance • Continual postcode change • Recoded and analysed postcode change in Manchester test area • Most changes: relabelling or splitting • Developments during course of project: • ONS to maintain postcode to OA directory • OS to create postcode boundary set RSS meeting: Nov 2000

  23. Current developments • ONS create own synthetic postcode polygons for input to OA design • NISRA digitize postcode polygons, then input to ONS OA design • Homogeneity – for consultation and final decision. NB different considerations in NI • GROS already have postcode polygons, but different OA design procedure (smaller OAs) RSS meeting: Nov 2000

  24. For further information • Project website: http://www.geog.soton.ac.uk/research/oa2001/ • For this presentation, follow: • Publications and resources • For demonstrator datasets, follow: • OA demonstrator RSS meeting: Nov 2000