Gridded population data for the UK

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Gridded population data for the UK

• redistribution models and applications

David Martin 20 February 2009
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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

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UK gridded data history.
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1971 census

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

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Small area data availability

• No grid-based data constructed from subsequent
  censuses
• Except in Northern Ireland (100m/1km 1971-2001)
• 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

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UK small area geographies

• Census

• Postcode

• Smallest zones enumeration districts (1971-91)
  and output areas (2001)
• Population size 3-400
• Single centroid coordinates, (digital boundaries
  1991, 2001)

• 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)

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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

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Centroids, boundaries and grids
Left centroid locations and boundaries Right
centroid populations redistributed onto grid
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Distance decay function
Always try to provide a caption next to your
picture in this style
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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

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1991 census

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

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(No Transcript)
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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

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

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

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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

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

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Mid-2006 grid map

• Produced by ONS using experimental small area
  data
• GISCO 1km grid not aligned with other UK products
• See poster!

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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