The future of output geography geography policy for NeSS

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The future of output geography - geography
policy for NeSS

• Robert Heyward
• ONS

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• Census Output
• Areas
• recap
• progress
• whats new?

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• Census Output Areas
• recap
• whats new ?
• outcome
• availability

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Output Areas - recap

• New for 2001 Census (EW), a geography
  specifically for low-level census outputs.
• approximately 175,000 OAs in England Wales
• align with administrative boundaries (Wards,
  Civil Parishes)
• built from unit postcodes on Census day. (April
  29th 2001) split for wards etc

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Output Areas - recap

• strong homogeneity of tenure and dwelling type
  within each OA
• size thresholds and targets
• synthetic but snapped where possible to road
  centrelines and administrative boundaries
• Scotland - similar but different approach
• Northern Ireland, postcodes gt same algorithm

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Output Areas - Whats new?

• improved shape
• now minimising distance between population
  centroids.
• improved boundaries
• to mean high water
• generalised (low resolution) sets
• eg for thematic display
• target size based on households
• with a minimum size for both population and
  households.

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Output Areas Achieved Size

• Hhlds
• Pop

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Output Areas - Outcome

• Achieved size within narrow range
• 95 OAs between 100 and 400 population
• only 1 above 500 population (eg university
  accommodation) (example figures for one city)
• boundaries much shaped by postcode and ward
  geography
• most OAs made up of 'whole' postcodes
• OAs at ward / parish boundary contain mixture of
  'whole' and split postcodes

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Output Areas - Availability

• Vector boundaries for OAs, (like the data),
  available free to ALL sectors
• Simple click-use terms
• ONS have paid all OS license fees for a period
  of 10 years
• Limitations on commercial repackaging - possible
  but talk to OrdSvy or Census CS
• Factsheet available

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Neighbourhood Statistics Geography Policy this
is what it means for users ..
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Geography Policy

• Emphasis on stability
• improving our ability to measure change over time
• Use of standard geographic units
• Grid reference
• Output areas
• Super Output areas
• Districts
• Statistics built from these blocks - or by
  estimation for other areas

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Geography policy

• Standard geographic units

Districts
Super OAs
Output Areas

• Frozen bases for data collection output

Grid reference
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Geography Policy for NeSS

• Output Areas (OA)
• Small - provide focus
• Stable - help with time series
• Stable - ease integration
• Stable - can act as a building brick
• Homogeneous - reflect the real world
• Help with disclosure
• Independent

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Geography Policy for NeSS

• Super Output Areas (SOAs)
• fill the gap in existing geographies between
  district and census output area
• comparability is easier as size is standardised,
  compared to present variation in size of wards
• helps to address disclosure control issues as
  OAs could be too disclosive
• enables ready comparison over time more stable
  than wards

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Geography Policy for NeSS

• SOAs - Hierarchy of Intermediate Layers
• Layer Size of Zone
• Output Area - 250 persons (average)
• Lower - 1,000 (minimum)
• Middle - 5,000 (min)
• Upper - 20,000 (min)
• District - 25,000 (and above)

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Geography policy
Districts

• Standard geographic units

Super OA 3
Super OA 2
Super OA 1
Output Areas

• Frozen bases for data collection output

Grid reference
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• Group of Output Areas
• Forming a lower level SOA

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• Group of Output Areas
• Forming a lower level SOA

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• Group of lower level SOAs
• Forming a middle level SOA

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• Group of middle level SOAs
• Forming an upper level SOA

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• Upper level SOAs
• Nest within the District

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Super OAs Design Issues

• Size variation within layer
• largest may be two (or three) times minimum size
• target size relative weighting of size and
  other factors
• target size in persons or households ?
• Relationship with Wards
• Lower layer - Nest
• data continuity Census Standard Tables
• Middle layer - Overlap
• more scope for homogeneity connectedness

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Geography policy
Districts

• Standard geographic units

Super OA 3
Super OA 2
Wards
Super OA 1
Output Areas

• What relationship ?
• What layer ?

Grid reference
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• If constrained to wards .
• variation in size means many wards will be one
  or two SOAs
• we get all the disadvantages of wards
• (not our ideal geography)
• If NOT constrained to wards
• - more complex disclosure issues
• BUT .

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• Even if we do constrain to wards the relationship
  only holds at the start ..
• Because SOAs are frozen and the wards within
  which they fit are not

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• If the SOAs are large (in terms of population)
• we lose the advantage of small focussed units
• (ward constraint can push size upwards)
• If the SOAs are too small
• we lose the advantage of these areas for
  avoiding disclosure

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Too big
Constrained to wards
Not constrained to wards
Too small
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The complicated relationship with wards

• Individual Output Areas nest within wards

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The complicated relationship with wards

• Individual Output Areas nest within wards
• The lower layer could also be constrained to wards

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The complicated relationship with wards

• But that does not mean that ALL layers have to be
  constrained
• Here the next layer is built from lower blocks
  but breaks wards

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The complicated relationship with wards

• This would be because the higher level area is
  more homogeneous than one built from wards

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SOAs Design Issues (contd)

• Shape / Connectedness
• down valleys NOT across mountains
• OS streets OA boundaries novel
• Homogeneity
• tenure, type of dwelling Additional Factors ?
• ONS classification of Output Areas
• Relative Weights / Balance
• greater weight to homogeneity / connectedness
• wider range of size within each layer

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Super OAs Process

• Census OA - Given Census 2001
• Lower - Zoning software
• Middle - Software / Appeal
• Upper - Suggestion / Software
• District - Given

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Super OAs Provisional Timing

• Feb to April - Feedback on Proposal - Feasibili
  ty Study
• May June - Review and Decision
• June July - Generate by Software
• August - Distribute
• Autumn 2003 - Appeals/Suggestions
• Winter 2004 - Publish

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Autumn Process - Sequence

• Local Agencies consider and agree
• (via Local Strategic Partnerships ?)
• potential modification to middle layer
• suggested composition of upper layer
• names for zones in all layers (if desired)
• separate target dates for each stage
• lower layer not open to modification

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Looking Ahead

• Collect and hold
• core geography
• Publish via web site
• core geography and
• user defined geographies, either
• ad-hoc
• popular, prepared

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Geography policy
Districts

• Standard geographic units

Super OA 3
Super OA 2
Wards
Super OA 1

• Frozen bases for data collection output

Output Areas
Grid reference
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• Outputs built from building blocks

An output built by adding up data collected for
the frozen block geography
Output of EXACT count-OAs, SOAs, LADs
Choose dataset(s)
Choose year(s)
Choose area
Output of BEST FIT ESTIMATE for area
An output built by estimating for an area that
isnt an exact fit to the blocks
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Geography Policy - Dissemination

• Data sets to 2001 referenced to 1998 ward and LA
  boundary
• Data from 2001 to 2003 to be built from counts
  for wards or output areas () and LA, boundaries
  at 31/12/02
• Data from 2004 - held for OA or SuperOA layer,
  district best fit to current () output
  geographies
• ( but)

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• Data referring to for 2001 to 2003
• For each data set, either wards or SuperOAs may
  be estimated, if necessary to prevent dual
  geography disclosure
• Data for 2004 onwards
• Counts for OAs, SuperOAs and district
• Estimates for current ward geography
  boundaries by SI at end of previous year

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Geography Policy for NeSS

• Issues
• will not collect or publish data on exact ward
  boundaries after 31/12/02
• outputs will be provided to changing boundaries
  by best fit techniques
• additional estimation techniques need to be
  developed
• assessing impact of estimation and disclosure
  control / rounding on data quality

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Examples of estimation - Census

• mainstream geography exact boundaries
• Census Ward, Parish, District, Govt Office Region
• Wards as known by 31.12.02 or anticipated
• other standard geographies estimated
• Parliamentary Constituencies etc
• estimated by aggregating CAS data from best fit
  of Output Areas
• National Parks, exceptionally,
• independently aggregated from grid referenced
  records

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Future Electoral Wards

• NeSS Prepared user defined geography
• estimated from OAs and SuperOAs
• estimates pre-calculated for ready access
• Synchronised date
• PAT-18 initiative now National Statistics policy
• As determined by Statutory Instruments laid
  before 31 December in previous year.
• Eg data for 2003 based on boundaries in SIs
  before 31.12.2002, (whether next elections in
  2003 or later)

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Summary
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Geography policy
Districts

• Standard geographic units

Super OA 3
Super OA 2
Wards
Super OA 1

• Frozen bases for data collection output

Output Areas
Grid reference
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• Outputs built from building blocks

An output built by adding up data collected for
the frozen block geography
Output of EXACT count-OAs, SOAs, LADs
Choose dataset(s)
Choose year(s)
Choose area
Output of BEST FIT ESTIMATE for area
An output built by estimating for an area that
isnt an exact fit to the blocks
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Further information and Contacts

• Super Output Areas
• - Proposal via
• http//www.neighbourhood.statistics.gov.uk/Informa
  tion_About_Ness.asp
• Feedback
• by end March, preferably
• end April, latest
• better.info_at_ons.gov.uk
• Robert Heyward 020 7533 6115
• Geography Policy
• better.info_at_ons.gov.uk

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