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

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Presentation on theme: "The future of output geography - geography policy for NeSS Robert Heyward ONS."— Presentation transcript:

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

2 Census Output Areas recap progress what’s new? Neighbourhood Statistics Geography Policy Super Output Areas

3 Census Output Areas recap what’s new ? outcome availability

4 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

5 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

6 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.

7 Output Areas: Achieved Size Hhlds Pop

8 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

9 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

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

11 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

12 Grid reference Output Areas Super OAs Districts Geography policy Standard geographic units ‘Frozen’ bases for data collection & output

13 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

14 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

15 Geography Policy for NeSS SOAs - Hierarchy of Intermediate Layers LayerSize of Zone Output Area-250 persons (average) Lower-1,000 (minimum) Middle-5,000(min) Upper -20,000 (min) District-25,000 (and above)

16 Grid reference Output Areas Super OA 1 Super OA 2 Super OA 3 Districts Geography policy Standard geographic units ‘Frozen’ bases for data collection & output

17 Group of Output Areas Forming a lower level SOA

18 Group of Output Areas Forming a lower level SOA

19 Group of lower level SOAs Forming a middle level SOA

20 Group of middle level SOAs Forming an upper level SOA

21 Upper level SOAs Nest within the District

22 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

23 Grid reference Output Areas Super OA 1 Super OA 2 Super OA 3 Districts Geography policy Standard geographic units Wards What relationship ? What layer ? ? ? ?

24 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 ….

25 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

26 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

27 Too big Too small Constrained to wards Not constrained to wards

28 Individual Output Areas nest within wards The complicated relationship with wards

29 Individual Output Areas nest within wards The lower layer could also be constrained to wards The complicated relationship with wards

30 But that does not mean that ALL layers have to be constrained Here the next layer is built from lower blocks but breaks wards The complicated relationship with wards

31 This would be because the higher level area is more homogeneous than one built from wards The complicated relationship with wards Similar characteristics

32 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

33 Super OAs : Process –Census OA-Given : Census 2001 –Lower-Zoning software –Middle-Software / Appeal –Upper-Suggestion / Software –District-Given

34 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

35 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

36 Looking Ahead Collect and hold –core geography Publish via web site –core geography and –user defined geographies, either ad-hoc popular, prepared

37 Geography policy Standard geographic units ‘Frozen’ bases for data collection & output Grid reference Output Areas Super OA 1 Super OA 2 Super OA 3 Districts Wards ? ? ?

38 Choose dataset(s) Choose year(s) Choose area 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

39 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 held for OA or SuperOA layer, & district best fit to current (*) output geographies (* but)

40 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

41 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

42 Examples of estimation - Census “ mainstream” geography : exact boundaries –Census Ward, Parish, District, Govt Office Region –Wards as known by 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

43 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 , (whether next elections in 2003 or later)

44 Summary

45 Geography policy Standard geographic units ‘Frozen’ bases for data collection & output Grid reference Output Areas Super OA 1 Super OA 2 Super OA 3 Districts Wards ? ? ?

46 Choose dataset(s) Choose year(s) Choose area 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

47 Further information and Contacts Super Output Areas - Proposal via –Feedback by end March, preferably end April, latest –Robert Heyward Geography Policy

48


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