Gridded population. redistribution models and applications. David Martin 20 February 2009

Transcription

1 Gridded population data for the UK redistribution models and applications David Martin 20 February 2009

2 Overview UK gridded data history (brief!) Small area data availability Grid-based modelling responses Applications and uses New small area data and the European Grid Map project 2

3 UK gridded data history.

4 1971 census Every form georeferenced 1km and 10km grid National census atlas CRU/OPCS/GROS (1980) People in Britain 4

5 Small area data availability No grid-based data constructed from subsequent censuses Except in Northern Ireland (100m/1km ) All other small area outputs for irregular zones Enumeration districts/output areas Improvements over time in spatial resolution, temporal frequency, directory products In general, population counts associated with coordinate references but uncertain spatial extents 5

6 UK small area geographies Census Smallest zones enumeration districts ( ) and output areas (2001) Population size Single centroid coordinates, (digital boundaries 1991, 2001) Postcode Smallest units full postcodes (since 1970s) Population size 50 (15 addresses) Single grid reference, no boundaries List of overlaps with census EDs, Oas (no direct match) 6

7 Grid-based modelling responses 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 and parameters possible experience suggests little gained by complexity 7

8 Centroids, boundaries and grids Left: centroid locations and boundaries; Right: centroid populations redistributed onto grid 8

9 Distance decay function Always try to provide a caption next to your picture in this style 9

10 Implementation Originally implemented as Fortran program (Sbuild) Source code shared with other researchers Set of national population models constructed for 1981, 1991 censuses and made available online (Surpop database) SurfaceBuilder Visual Basic 6 code developed for 2001 census and downloadable for research use 10

11 1991 census 200m model of south east England population density Constructed from census enumeration district centroids and counts Built with SurfaceBuilder 11

12 12

13 Applications and uses: examples Use both of national reference models from Surpop and Sbuild/SurfaceBuilder software by researchers using own data Applications which require detailed model of spatial population distribution, settlement pattern, accessibility drive times, hazard exposure Novel applications and visualizations which develop analyses only possible using grid-based models 13

14 East Anglia population model for modelling predicted visitor rate function (Brainard et al., 1997, Journal of Transport Geography)

15 Visualization of population landscapes Wood et al., 1999, Environment and Planning B) 15

16 Applications and uses: advantages Zonal geography weak for visualization Data collection zones as inappropriate analysis units for sparse populations Need maximum spatial information for calculation of distances, populations at risk, etc. Difficulties appropriately integrating zonal populations with environmental information Gridded geographies many advantages for comparison between countries and through time 16

17 New small area data and the European Grid Map project.

18 Direct aggregation from experimental data ONS producing new small area population estimates Experimental data, annual estimates using census updated from administrative sources Published for lower super output areas but internally modelled for postcodes Direct aggregation permits production of 1km grid square estimates and generation of grid map Data precision overcomes many earlier methodological difficulties over choice of distance decay function etc. 18

19 Mid-2006 grid map Produced by ONS using experimental small area data GISCO 1km grid not aligned with other UK products See poster! 19

20 Further work Aggregation from small area estimates: no direct disclosure control challenges from modelled data: may not be possible to use same method with 2011 census data Challenge of GISCO grid for UK users: incompatible with national mapping products Simplistic aggregation assumes all population of postcode falls in same grid cell: need to consider redistribution model, edge effects Potential for modelling distribution at higher resolution within cells 20