"Flow data involve flows of individuals in the UK between origins and destinations"
What are flow data?
Flow data (sometimes called 'interaction' or 'mobility' data) involve flows of individuals in the UK between origins and destinations. These flows are either the residential migrations of individuals from one place of usual residence to another or of commuters making journeys from home to workplace.
Census flow data are derived from the questions on the census form relating to place of usual residence one year ago, the place of work for the respondent’s main job and, from 2011, if a respondent spends more than 30 days a year at a second address. These flow data are currently available at a range of different spatial scales for the 1981, 1991, 2001, and 2011 Censuses.
As flow data feature both a start and end point, this means that tables are often much larger and more complex than for other census data. For example, a cross-tabulation that showed the counts of migration flows from all of the 8850 Census Area Statistics (CAS) wards in England and Wales in 2001 to all others, would create an origin-destination table with 78,322,500 cells. A similar table for 2001 Output Areas would have 30,777,088,356 cells, the vast majority of which would contain zeros!!
What can flow data tell us?
Flow data are of unique significance as they tell us not only where individuals are moving and commuting from and to, but also some of the characteristics of these people.
Data on migration can tell us how the numbers and characteristics of populations are changing in different locations – information of vital importance for central and local government planning for health, education, housing and other key services.
As well as informing us about area specific patterns, migration data from the census are also able to tell us, for example, the movement propensities of different ethnic, age, gender, socio-economic and family status groups in the UK, allowing us to explore the socio-spatial evolution of different sections of society. Similarly, flow data on commuters to work can reveal not just the characteristics of different commuters but also the locations that these commuters travel to and from, the distances involved, as well as their preferred method of transport. Furthermore, the time-series of flow data available digitally from the last four censuses can tell us how these migration and commuting patterns have changed over time. The map below illustrates the flows of in-migrants to Cardiff in the 12 month period before the 1991 Census from other districts in South Wales, from other counties in the rest of Wales, from other regions in the UK, from Eire and from the rest of the world
Migration to Cardiff (1991 SMS Set 2, Table 1)
1991 Census Special Migration Statistics, Crown Copyright
Using the WICID data extraction facility, it is possible to select data for a range of different origin and destination geographies (which do not need to match) for any areas in the UK.
Researchers interested in local and national patterns of student migration to higher education institutions, for example, would be able to obtain data that provides counts of all males aged 18-24 who moved into the University ward in Leeds from other wards in the Leeds Metropolitan District, from other districts in West Yorkshire and from other regions in the UK, in 2001.
Obtaining the data
The UK Data Service Census Support facilitates access to the interaction data for members of UK Higher Education institutions. Access is provided through WICID – the Web-based Interface to Census Interaction Data.
Access is free to all registered users, with WICID enabling users to download customised data in a number of different formats. For users who are unfamiliar with the WICID interface, the website provides links to tutorials and training materials. Access to a library of common queries is also available, which enables users to download data quickly without the need to go through the query building process.
What data are available?
Currently WICID provides access to data from the 1981, 1991, 2001 and 2011 Censuses. It is also possible to access other non-census flow datasets such as a time-series of post-2001 migration flows derived from NHS patient registers. The entirety of 2011 Census open and safeguarded data has been added with more than 220 tables currently being available. Access to the 2011 datasets is either ‘public’ or ‘safeguarded’ depending on the level of geography and variables. Public datasets are open to any users via Open Government Licence (OGL) without the need to register or login. Safeguarded datasets are available via UKDS to members of academia, local and central government, NHS, and UK parliaments and assemblies via End User Licence (EUL) and user will need to have an active institutional account to be granted access.
The datasets currently held include:
Census migration datasets:
2011 Census: Special Migration Statistics (Local Authority District, Ward and Output Area level)
2001 Census: Special Migration Statistics (Levels 1, 2 & 3 + Level 2 Scotland Postal Sectors). Migration data at District, Ward, Scottish Postal Sector and Output Area level
1991 Census: Special Migration Statistics (Sets 1 [including re-estimation for 2001 boundaries] & 2, MIGPOP, SMSGAPS and SAS LBS Table 100 A & B). Migration data at Ward and District level; Ward level re-estimations for 2001 geographies
1981 Census: Special Migration Statistics (Set C and 1981 county/regional Geography). Ward level migration data re-estimated for 1991 and 2001 boundaries. County/region level data for 1981
Census commuting datasets:
2011 Census: Special Workplace Statistics (Local Authority districts, Middle-Layer Super Output Area, Intermediate Zone for Scotland, Workplace Zone for England and Wales, and Outpur Area level)
2001 Census: Special Workplace Statistics (Levels 1, 2 & 3). Commuting data at District, Ward and Output Area scales
2001 Census: Special Travel Statistics (Level 1, 2 & 3 + Level 2 Scotland Postal Sectors). Commuting data for Scotland at Council Area, Ward, Postal Sector and Output Area Scales
1991 Census: Special Workplace Statistics (Sets A, B and C [including modified set Cs]). Commuting data by residence (A) Workplace (B) and within & between wards (C) for 1991 and 2001 boundaries
1981 Census: Special Workplace Statistics (Set C and 1981 county/ regional Geography). Ward-level migration data re-estimated for 1991 and 2001 boundaries. County/region level data for 1981
Variables that can be selected from these datasets may include:
Family status of migrant
Whether suffering limiting long-term illness
Whether in household
Moving groups by tenure
Moving groups by NS-SEC of group reference person
Migrants in Scotland/Wales/Northern Ireland with some knowledge of Gaelic/Welsh/Irish
Method of travel to work
A book covering everything to do with census flow data has recently been published:
Stillwell, J., Duke-Williams, O. and Dennett, A. (eds.) (2010) Technologies for Migration and Commuting Analysis: Spatial Interaction Data Applications. Hershey: IGI Global.
Many other papers and book chapters have been written on flow data, a small selection of which are as follows:
Champion, T. (2005) ‘Population movement within the UK’, in R. Chappell (ed.) Focus On People and Migration, Basingstoke: Palgrave Macmillan, pp. 92-114.
Champion, T. and Coombes, M. (2007) ‘Using the 2001 Census to study human capital movements affecting Britain's larger cities: insights and issues’, Journal of the Royal Statistical Society Series A (Statistics in Society), 170(2): 1-20.
Champion, T., Coombes, M., Raybould, S. and Wymer, C. (2007) Migration and Socio-economic Change: A 2001 Census Analysis of Britain's Larger Cities, Bristol: The Policy Press.
Dennett, A. and Stillwell, J. (2011) ‘A new area classification for understanding internal migration in Britain.’ Population Trends, 145: 146-171.
Dennett, A. and Stillwell, J. (2010) ‘Internal migration in Britain, 2000-01, examined through an area classification framework.’ Population Space and Place, 16(6): 517–538.
Duke-Williams, O. (2000) Designing zoning systems for flow data, In Atkinson, P amd Martin, D. (eds.) GIS and GeoComputation: Innovations in GIS 7, London: Taylor and Francis, pp. 115-134.
Fielding, T. (2012) 'Migration in Britain Paradoxes of the Present, Prospects for the Future, Cheltenham: Elgar.
Rees, P. and Duke-Williams, O. (1995) The story of the British Special Migration Statistics, Scottish Geographical Magazine, 111 (1):13-26.
Rees, P., Thomas, F., and Duke-Williams, O. (2002) ‘Migration data from the Census’ in P. Rees, D. Martin, and P. Williamson (eds.) The Census Data System, London: Wiley, pp. 245-268.
Stillwell, J. (2006) Providing access to census-based interaction data in the UK: that’s WICID, The Journal of Systemics, Cybernetics and Informatics, 4(4): 63-68.
Stillwell, J. (2006) Using WICID (Web-based Interface to Census Interaction Data) in the classroom, The Journal of Systemics, Cybernetics and Informatics, 4(6):106-111.
Webinar recording: 2011 Census - Flow Data
Recording of webinar held on 7 December 2015
This webinar provided an overview of the interaction data available as outputs from the 2011 Census.