Getting the Foundations Right: Spatial Building Blocks for Official Population Statistics

When publishing official population statistics, many national statistical organisations define small areas termed ‘building blocks’ which are then aggregated into larger ‘output zones’ for data release. While output zones are known to have enormous influence on spatial analysis, there has not been any systematic analysis of the effect of building blocks on characteristics of output zones. This paper evaluates current international practice in building block design, identifying key conceptual and practical issues. Using the example of six local authorities in England and Wales, it employs automated zone design to evaluate the influence of two sets of building blocks (street blocks and postcodes) on output zone characteristics. Household-level census data, accessed under secure conditions, are used to evaluate the impact on both newly designed and maintained output zones. Postcodes are shown to be more effective building blocks than street blocks, providing more uniform population and household sizes, greater precision for matching postcoded data to census data, and enabling more zones to be maintained. However, street blocks deliver more compact output zones and greater internal homogeneity of tenure and accommodation type. The scale effect of the modifiable areal unit problem and the specific geographical patterning of variables are both shown to be important factors when designing building blocks. These findings have directly informed policies and processes for the 2011 Census in England and Wales and provide useful conceptual and practical guidance for any national statistical organisation or analyst designing their own building blocks. The paper concludes that some aspects of international building block design practice could be more effectively harmonised but that such design should always be nationally specific to incorporate locally varying conceptual and practical issues. Further research should extend this analysis to other building block types, notably grid squares.