January 2007

A hybrid solution to the question of stability or redrawing has been offered by one or two people.  This hybrid is arrived at from a viewpoint that sees the merits of keeping Super Output Areas stable, but that is less sure about Output Areas.  I'd like to investigate this a bit.

I'll try and summarise the thinking behind the solution offered.  Apologies if I don't do it justice.  Corrections welcomed!

Apart from the 2001 Census, few data sources have been made available to ONS for publication at the OA level.  Outputs and data definitions for the next Census have yet to be defined.  It is possible that Census indicators of change at a level as small as OAs could be rendered invalid as a result of any changes to data definitions.  Given these points, OAs could be entirely redrawn within stable Lower Layer SOA (LSOA) boundaries and be based on Census 2011 data.  SOA time series data would therefore be safeguarded.

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OAs were specifically designed to have a strong relationship with postcode geography.  Census 2001 enumerated postcodes were the building blocks used in the construction of OAs.  Only where postcodes straddled ward, parish (England), and community (Wales) boundaries, were they split into more than one OA polygon.  This affected approximately 2.5% of all enumerated unit postcodes.

The boundary set that resulted was irregular, but the postcode foundations of the geography were considered important for data linkage purposes.

As with administrative geographies, postal geography moves around over time.  It is a convenient, rather than ideal, geography for statistical purposes.  Ideally data records would be geo-referenced to addresses or grid references, and lookups from these would be easy to produce and distribute.  But further progress in this direction is still needed.  The desire has not yet proved strong enough to facilitate necessary data developments.

The consultation asks whether OA boundaries should be neatened to real world features.  This could be achieved by snapping them to, for example, OS MasterMap.

OA boundaries are largely abstract.  They were built up from artificial Thiessen polygons drawn around 2001 Census addresses.  As a result they cut across all other real world features, as do SOA boundaries further up the hierarchy.

Justin Martin picked up on this earlier in the blog and posted a comment.  He's keen to see a more coherent hierarchy of geographies down to individual features (or TOIDS).  There's clearly a potential data licensing issue here, but is this something worth investigating further?  What might the benefits be?