Join us
Orange welcome sign that reads Royal Geographical Society with IBG.

Become a member and discover where geography can take you.

Join us



As a result of a new geospatial methodology for small geographical output areas (OAs) in the 2011 UK Census, government, businesses and communities are better able to make decisions, save money or enhance profits, and target services and other support more effectively to the geographical areas or population groups that need them.



Every ten years since 1801 (except 1941) there has been a national UK census, collecting data on the location and characteristics of households, including the type of property and who lives there, where people work and how they get there and other socio-economic characteristics such as income, health and ethnicity. Although the same questions are asked across the whole country, geographical areas could not be compared spatially or over time because enumeration districts varied in size and boundaries changed over time.



Professor David Martin (University of Southampton) developed a technique for the 2001 Census that enabled local areas to be assessed on a more directly comparable like-for-like basis. This was done by creating small geographical ‘building blocks’ from which census data is aggregated and reported independent of the enumeration districts.

Professor Martin created an automated method in which 200,000 small geographical Output Areas of around 300 people each are generated based on postcode “territories”. OAs can be grouped into larger areas such as Super Output Areas for comparison at larger scales.

Output Areas have a consistent population size, reasonable homogeneity of households, and are updated in response to population changes. This means that patterns of inequalities, ethnicity and housing are more easily identified and tracked over time. The ONS provides a resource which converts wards to Output Areas. Thisis useful because while larger local government wards are sometimes used as a unit for statistics, but the boundaries change irregularly and are based on the distribution of registered electors within local authorities rather than selected population characteristics.

Output Areas have been pivotal to the Census methodology and contemporary population geography in the UK since their first use in the national census of 2001. They were enhanced and updated for the 2011 Census, and now include workplace zones for the publication of data about workers and workplaces. The ONS will use output areas in the 2021 census as the lowest geographical area at which estimates are provided, providing the basic structure for how census data is shared, interpreted and used to make decisions.



Better decisions

Output Areas have become the fundamental building block not just of census data but of demographic location-based data analysis in the UK. Linking and comparing information by its location enables analysis and decision-making that better recognise variation and similarities between places, which in turn allows for more precisely targeted policy interventions or decision-making.

The applications of OAs as a structure for data and a tool for informing decision-making are myriad. The RGS-IBG’s 2014 collection of short case studies on applications of small area census data outlines a number of applications. These include:

  • Bristol Council used data on tenure patterns to allocate affordable housing resources to deprived areas, and used small area data to estimate the prevalence of women subjected to FGM and target advocacy and support to end the practice.

  • The Health and Safety Executive integrates OA-level data into OS mapping to help model and assess risk at hazard sites, including Sellafield.

  • Market research companies use OAs in market research classification, including identifying sites for shops and localising newspaper advertising

Output Areas have also enabled NHS Digital to structure large datasets generated from healthcare institutions across the country, allowing disparate indicators and datasets to be aligned and analysed on a geographical basis. This supports the targeting and delivery of healthcare, and helps identify how and why health outcomes vary spatially.

Well-structured data can also be used to improve public access to useful information -  from 2014 to 2017, the Office for National Statistic’s Neighbourhood Statistics Service delivered data via a web-based data explorer, to support school governors, GPs, church volunteers, charity workers and others in better understanding their local communities. These data are still available via the ONS and NOMIS.

Businesses and researchers have built innovative and informative applications and websites structuring data using Output Areas, such as the UCL and ESRI-created Datashine website (below), which maps 2011 census statistics for the public to explore and use.



Combining systems / data

Output areas are ubiquitous in systems and projects which use demographic data in the UK. Professor Martin’s work underpinned the creation of the 2001 census output geographies which have been the basis of the 2001, 2011 and 2021 censes.

With Dr Sam Cockings and Andrew Harfoot (University of Southampton), this work yielded the AZTool, a publically-available software package which can be used to generate Output Areas from “Enumeration Districts” according to other parameters such as population and age distribution. This was used in the development of the UK 2011 census, enabling the collection and analysis of raw demographic data collected in the census. AZTool and OAs then underpinned the group’s creation of Workplace Zones, a geographical framework developed with the ONS and DfT for workplace-related data.

The work has now been extended to near-real-time population modelling using OAs as centroids, and beyond into dynamic time-specific population modelling and near-real-time modelling to improve security and emergency responses. These tools and implementations fundamentally improve the interoperability, visualisation potential and understanding of population data.


Further reading

The RGS-IBG's briefing with output area and small area data case studies

 ONS’ introduction to output areas

AZTool is open access and available for use

Learn more about the work of the Geodata group within the Department of Geography at the University of Southampton


Share this case study

This is an open access article under the terms of the Creative Commons Attribution License (CC BY NC 4.0), which permits use, adaptation, distribution and reproduction in any medium or format, provided the original work is cited and it is for non-commercial purposes. Please contact us for other uses.


How to cite

Royal Geographical Society (with IBG) (2019) Revolutionising the census with new methods for population data in the UK. Available at: Last accessed on: <date>