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High resolution and local scale: national population surface models from the UK Censuses

High resolution and local scale: national population surface models from the UK Censuses. David Martin Department of Geography University of Southampton. High resolution and local scale: overview. UK data context 1971-2001 Need for non-zonal representations Redistribution model

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High resolution and local scale: national population surface models from the UK Censuses

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  1. High resolution and local scale: national population surface models from the UK Censuses David Martin Department of Geography University of Southampton

  2. High resolution and local scale: overview • UK data context 1971-2001 • Need for non-zonal representations • Redistribution model • Implementation • Applications • Future directions • Key references

  3. UK data context 1971-2001 • Basic spatial unit for census output: enumeration district (ED) mean c. 400 population • 100m population-weighted centroid • 1991- improved spatial resolution and (imperfect) link to postal centroids • no cadastral mapping, no large-scale digital land use mapping

  4. Need for non-zonal representations • Wide variations in ED size and shape • Space-filling, hence including extensive unpopulated areas • Large-scale redefinition of EDs (68% 1981-91)

  5. Redistribution model (1: basics) • Population-weighted centroid(s) as summary points of local distribution • Locally adaptive kernel estimation based on inter-centroid distances • Redistribution of centroid counts into grid: spatially discontinuous model • Various derivatives, including constraint to zone boundaries (1991- only)

  6. Redistribution model (2: function) Weighting wij a Distance dij k

  7. Redistribution model (3: example) Centroids and boundaries Gridded population model

  8. Implementation (1: data) • 10/100m ED centroids and counts • 200m grid • 250m initial search radius • simple distance decay model • no ED boundaries • national models (c 155,000 centroids) • FORTRAN now, Visual Basic to follow...

  9. Implementation (2: example) • 300 x 300 km extract from national population model of UK based on 1991 Census

  10. Implementation (3: extensions) • Reallocate ED data onto 100m postcode locations in proportion to household counts, (c. 15 postcodes per ED) • Constraint to zone boundaries where available - preserves zonal populations (at grid resolution)

  11. Applications (1: examples) • Ancillary layer in urban satellite image interpretation (eg. Mesev et al, 1995) • Population base for distance-sensitive applications (eg. Lovett et al, 1997) • Basis for intercensal comparison (eg. Bracken and Martin, 1995) • Non-UK data with no boundaries

  12. Applications (2: visualization) • Visualization of population ‘landscapes’ • (eg. Wood et al, 1999)

  13. Applications (3: distance models) • East Anglia population model for modelling predicted visitor rate function • (eg. Brainard et al, 1997)

  14. Future directions • 2001: Census design using GIS • 2001: new, smaller output areas, stronger link to postal geography • Potential for error estimation and model calibration from sub-threshold census data • International applications? (eg. Australia)

  15. Key references • Martin, D. (1989) Transactions IBG • Bracken, I. and Martin, D. (1995) E&P a • Martin, D. (1996) IJGIS • http://census.ac.uk/cdu/surpop

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