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Automated zone-design methods are increasingly being used to create zoning systems for a range of purposes, such as the release of census statistics or the investigation of neighbourhood effects on health. Inevitably, the characteristics originally underpinning the design of a zoning system (eg, population size or homogeneity of the built environment) change through time. Rather than designing a completely new system every time substantive change occurs, or retaining an existing system which will become increasingly unfit for purpo.se, an alternative is to modify the existing system such that zones which still meet the design cdteda are retained, but those which are no longer fit for purpose are split or merged. This paper defines the first generic methodology for the automated maintenance of existing zoning systems. Using bespoke, publicly available, software (AZToof), the methodofogy is empfoyed to modify the 2001 Census output geographies within six local authority distdcts in England and Wales in order to make them suitable for the release of contemporary population-related data. Automated maintenance of an existing system Is found to be a more Iterative and constrained problem than designing a completely new system; design constraints frequently have to be relaxed and manual intervention is occasionally required. Nonetheless, existing zone-design techniques can be successfully adapted and implemented to automatically maintain an existing system. The findings of this paper are of'direct relevance both to the Office for National Statistics in their design of the 2011 Census output geographies for England and Wales and to any other countdes or organisations seeking to maintain an existing zoning system.

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Benzene is classified as a group 1 human carcinogen by the International Agency for Research on Cancer, and it is now accepted that occupational exposure is associated with an increased risk of various leukaemias. However, occupational exposure accounts for less than 1% of all benzene exposures, the major sources being cigarette smoking and vehicle exhaust emissions. Whether such low level exposures to environmental benzene are also associated with the risk of leukaemia is currently not known. In this study, we investigate the relationship between benzene emissions arising from outdoor sources (predominantly road traffic and petrol stations) and the incidence of childhood leukaemia in Greater London. An ecological design was used because of the rarity of the disease, the difficulty of obtaining individual level measurements of benzene exposure and the availability of data. However, some methodological difficulties were encountered, including problems of case registration errors, the choice of geographical areas for analysis, exposure measurement errors and ecological bias. We use a Bayesian hierarchical modelling framework to address these issues, and we investigate the sensitivity of our inference to various modelling assumptions.

The paper addresses problems arising from the representation of workplace population data by using geographical areas based on residential locations. This widespread international practice detrimentally affects publication of census workplace data. A novel solution is proposed for the creation of new workplace zones by using automated zone design techniques and is applied to five prototype areas by using England and Wales 2001 census microdata. Particular workplace-based disclosure control challenges are addressed and the characteristics of the proposed workplace zones reviewed. This approach offers important benefits for the international reporting of workplace data and is currently being incorporated in England and Wales 2011 census output plans.