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Exact-fit and best-fit estimates

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Statistical tables and outputs from the 2011 Census will be exact-fit estimates for the following geographies:

  • output areas, 2011

  • lower layer super output areas, 2011

  • middle layer super output areas, 2011

  • local authorities, including local authority districts and unitary authorities counties, current on 31 December 2011

  • national parks, current on 31 December 2011

Best-fit and the National Statistics Geography Policy

An overall aim of the 2011 Census is to provide outputs in line with the National Statistics (NS) Geography Policy. The policy sets out the principles for using geographic information to produce and disseminate statistics. Its principles are driven by the following objectives to: 

  • reference statistical events accurately, consistently and at as low a level of geographical referencing as possible

  • maximise the comparability of national statistics

  • minimise the impact of changing area boundaries on national statistics outputs

  • provide the framework for defining and standardising how geographies and associated information are defined, used and presented in the production of statistics

A central element of the NS Geography Policy is that:

“Source data must be referenced to other geographies on the basis of its stable small area building block “best-fitted” to those geographies when creating National Statistics outputs.”

And that:

“In England, Wales … the small area building blocks are the output areas and super output areas”.

As a result, estimates for all other geographies above output areas will be best-fitted from geographies current on 31 December 2011. The best-fit from output areas to higher geographies is determined by plotting the (population weighted) centroid of each output area to the boundary of the higher geography.

Best-fitting from output areas helps ensure that census statistics are non-disclosive and consistent with all national statistics produced using the best-fitting method.

Learn more about exact-fit and best-fit methods.


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