The future of output geography - geography policy for NeSS Robert Heyward ONS.

The future of output geography - geography policy for NeSS

Robert Heyward

ONS

Census OutputAreas• recap• progress• what’s new?

Neighbourhood StatisticsGeography Policy

Super Output Areas

Census Output Areas• recap

• what’s new ?• outcome

• availability

Output Areas - recap

• New for 2001 Census (E&W), 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

• 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 > same algorithm

Output Areas - recap

Output Areas - What’s 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.

Output Areas: Achieved Size

• Hhlds

• Pop

0

10000

20000

30000

40000

50000

60000

70000

40 - 49 50 - 59 60 - 69 70 - 79 80 - 89 90 - 99 100 -109

110 -119

120 -129

130 -139

140 -149

150 -159

160 -169

170 –179

180 -189

190 -199

200+

Household range

0

10000

20000

30000

40000

100 -124

125 -149

150 -174

175 -199

200 -224

225 -249

250 -274

275 -299

300 -324

325 -349

350 -374

375 -399

400 -424

425 -449

450 -474

475 -499

500+

Population range

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

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

Neighbourhood Statistics

Geography Policy

this is what it means for users …..

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

Grid reference

Output Areas

Super OAs

Districts

Geography policy• Standard geographic units

• ‘Frozen’ bases for data collection & output

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


• 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


• 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)

Grid reference

Output Areas

Super OA 1

Super OA 2

Super OA 3

Districts



• Group of Output Areas

• Forming a lower level SOA

• Group of lower level SOAs

• Forming a middle level SOA

• Group of middle level SOAs

• Forming an upper level SOA

• Upper level SOAs

• Nest within the District

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

Grid reference

Output Areas

Super OA 1

Super OA 2

Super OA 3

Districts


Wards

• What relationship ?

• What layer ?

?

?

?

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 ….

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

• Individual Output Areas nest within wards

The complicated relationship with wards

• Individual Output Areas nest within wards

• The lower layer could also be constrained to 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


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


Similarcharacteristics

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

Super OAs : Process

– Census OA- Given : Census 2001– Lower - Zoning software– Middle - Software / Appeal– Upper - Suggestion /

Software– District - Given

Super OAs : Provisional Timing

• Feb to April- Feedback on Proposal- Feasibility Study

• May & June - Review and Decision• June & July - Generate by Software• August - Distribute• Autumn 2003 - Appeals/Suggestions• Winter 2004 - Publish

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

Looking Ahead

• Collect and hold– core geography

• Publish via web site– core geography and – user defined geographies, either

• ad-hoc• popular, prepared



Grid reference

Output Areas

Super OA 1

Super OA 2

Super OA 3

Districts

Wards ?

?

?

Choosedataset(s)

Chooseyear(s)

Choosearea

Output of EXACT

count-OAs, SOAs, LADs

Output of BEST FIT ESTIMATE

for area

An output built by adding up data collected for the frozen block geography

An output built by estimating for an area that isn’t an exact fit to the blocks

• Outputs built from building blocks

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)

• 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


• 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

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

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)

Summary



Grid reference

Output Areas

Super OA 1

Super OA 2

Super OA 3

Districts

Wards ?

?

?

Choosedataset(s)

Chooseyear(s)

Choosearea

Output of EXACT

count-OAs, SOAs, LADs

Output of BEST FIT ESTIMATE

for area

An output built by adding up data collected for the frozen block geography

An output built by estimating for an area that isn’t an exact fit to the blocks

• Outputs built from building blocks

Further information and Contacts

• Super Output Areas - Proposal viahttp://www.neighbourhood.statistics.gov.uk/Information_About_Ness.asp

– Feedback• by end March, preferably• end April, latest

– [email protected]– Robert Heyward 020 7533 6115

• Geography Policy– [email protected]

The future of output geography - geography policy for NeSS Robert Heyward ONS.

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