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Digitised boundary datasets |
What are digitised boundary datasets?
Census area statistics (CAS) provide counts of people or households for
geographical areas broken down by socio-demographic characteristics such as age,
gender or employment. Digitised boundary datasets (DBDs) are a digitised representation
of the underlying geography of the census.
Copyright statement:
Source: 2001 Census Output Area Boundaries. Crown copyright 2003. Crown copyright material is reproduced with the permission of the Controller of HMSO.
The geography of the census consists of a hierarchical subdivision of UK local government
areas of various types down to sub-authority areas, such as wards, to lower levels created
specifically for census purposes such as enumeration districts or output areas.
For example, the geography of the 1991 census for England consisted of a 4-level hierarchy:
enumeration districts (EDs) at the lowest level nest within wards, districts and counties.
A similar system was used in 1981 and most recently for the 2001 census.
Copyright statement:
This work is based on data provided with the support of the ESRC and JISC and uses boundary material which is copyright of the Crown and the ED-LINE Consortium.
The co-ordinates which make up these census geographies are available as digitised boundary datasets.
What can digitised boundary datasets tell us?
Census area statistics contain a pointer to the geographical census areas to
which they relate. By linking census area statistics with the corresponding
digitised boundary datasets for a specific census year, the census attributes can
be visualised as a map. Mapping census datasets in this way allows for an exploration
of the characteristics of census datasets geographically and may provide additional
demographic, socio-economic and cultural insights into the census data.
As an example, it is possible to explore the patterns of housing tenure recorded in
the census - such as the proportion of people who live in local authority housing.
By linking the census statistics to DBDs of county boundaries or enumeration districts
within a specific region and producing a shaded choropleth map of the numerical values
held in the census dataset, it can be shown how housing in one region differs from another
and whether there are any interesting patterns in the geographical distribution of census
variables.
Copyright statement:
Source: 2001 Census Output Area Boundaries. Crown copyright 2003. Crown copyright material is reproduced with the permission of the Controller of HMSO.
Using the census statistics and boundaries in a Geographical Information System (GIS) allows for spatial analysis of the census data and its combination with other non-census geographically referenced datasets.
Digitised boundary datasets can be used for:
- map production for research articles
- data synthesis and development of residential neighbourhoods
- geostatistical analysis of demographic or employment change
- small area analysis and deprivation studies
- health care research – incidence mapping and analysis
- historical demographic research
The geography of the decennial census is not fixed. For the same local
area the output geography used in the 1971, 1981, 1991 or 2001 census
may be quite different.
Copyright statement(s):
This work is based on data provided with the support of the ESRC and JISC and uses boundary material which is copyright of the Crown and the ED-LINE Consortium.
&
Source: 2001 Census Output Area Boundaries. Crown copyright 2003. Crown copyright material is reproduced with the permission of the Controller of HMSO.
Different research questions may require mapping of the same
census statistic at different scales and in different locations.
Copyright statement:
This work is based on data provided with the support of the ESRC and JISC and uses boundary material which is copyright of the Crown and the ED-LINE Consortium.
Obtaining the data
The
UKBORDERS data support unit provides facilities by which researchers
can access a full collection of digitised boundary datasets and supporting
datasets, including geographic look-up tables. These datasets are available
either pre-packaged or through a dynamic user-driven interface permitting
user-defined selection of boundaries.
The easy download facility provides access to the most regularly requested
boundaries as ready-to-use national datasets.
The boundary data selector facility allows users to select boundaries for
the area required, for the census year required, and in the data format required.
This flexibility allows the researcher to download census output areas for several
counties or for a specific ward or district. During the boundary selection process,
the chosen boundaries can be previewed over a topographic back-drop map before
finally being extracted in one of several data formats for use with different GIS
and mapping packages.
What data are available?
Many boundary types are available for England, Wales, Scotland (1840 to 2003) and
Northern Ireland (2001 data only) including:
- Administrative boundaries (eg. districts, unitary authorities, health boundaries etc.)
- Census boundaries (2001, 1991, 1981 and 1971 census boundaries for use with census statistics)
- Electoral boundaries (e.g wards, parliamentary constituencies)
- Environmental boundaries (e.g. national parks, urban footprints)
- Postal boundaries (postcode-related boundaries)
- Historical boundaries (pre-1971 census and administrative boundaries from 1840 onwards)
- Other boundaries (e.g. synthetic neighbourhood localities)
Important supporting datasets include geographic look-up tables. These include the
latest versions of the National Statistics Postcode Directory (NSPD) from National
Statistics. The NSPD provides details of the locations of current and historic
postcodes along with details of other geographic areas in which the postcode is
located. This dataset provides a valuable means by which events or occurrences
(such as disease, crimes, customer residence etc) can be allocated from a postcode to
another area such as an electoral ward or health area.
Special Conditions
Access to digitised boundary datasets and look-up tables requires acceptance by registered users of
additional special conditions. Principally these restrict use of the digitised boundary
datasets and associated data to teaching and research.
Integrated 2001 Census Digitised Boundary Data
The Census Dissemination Unit's
Casweb
service can provide users with digital boundary data to accompany 2001 census data downloads in a range of standard
GIS formats ready for mapping and spatial analysis. The data are available in ESRI Shape, Mapinfo Tab and Mid/Mif and
also GML. Other formats may also be released if there is a user requirement for them.
In order to accommodate the boundary data at Output Area level, which in its raw format for England alone is 1.3Gb,
a data reduction technique called generalisation (or generalization) is used. Generalizing boundary data makes the
polygons less intricate and therefore require less points to describe them. For Scotland, Wales and Northern Ireland
the data is taken from a generalised boundary dataset created by UKBORDERS. For England the CDU have created a
generalised boundary data set using the same
Douglas-Peucker
algorithm employed by UKBORDERS at Output Area.
Further reading
UK census geography:
Rees P., Martin D.M. and Williamson P. (2002)
The census data system, Chichester: Wiley.
ONS (2007)
Beginner’s guide to UK geography
General Register Office for Scotland (2007)
Geography
Geo-Refer (2007)
Geographical referencing for social scientists: a practical workshop
Handling spatial data and geographical information systems:
Walford, N. (2002)
Geographical data: characteristics and sources, Chichester: Wiley.
Martin, D. (1996)
Geographic information systems: socioeconomic applications,
London: Routledge.
Monmonier, M. (1996)
How to lie with maps, Chicago: University of Chicago Press.
Longley P.A., Goodchild M.F., Maguire D.J. and Rhind D.W. (2001),
Geographic
information systems and science, Chichester: Wiley.