Census 2001 - Metadata

Geography

Standard output will be available for a range of areas as defined on Census day 2001.

The 566 Wards used for the 1991 Census were created following the Boundary Commission Review in 1984.  They do not compare very well with the 582 wards used for the 2001 Census which were created following the 1992 Boundary Commission review as there is significant differences between the sets.  For 1992, many of the 1984 individual ward boundaries were changed, others were deleted and subsumed into existing or new wards and some were renamed.

The only major change in District Council boundaries between the two Censuses relates to Banbridge and Newry and Mourne District Council areas where as a result of the Local Government District Boundary change of 1992 the ward of Rathfriland, in effect, moved from Newry and Mourne Local Government District to Banbridge Local Government District.

Area types

The main types of existing areas which the Census recognises are: Ward, Local Government District, Health and Social Services Boards, Education and Library Boards, Parliamentary Constituency and NUTS level 3.   All have boundaries which are currently consistent with one another although they are subject to change over time.

Geographical referencing

Census data are aggregated within different boundaries essentially by assembling small geographical building bricks to which the data are coded. The most adaptable and unchanging building brick is the Irish Grid co-ordinate reference. A reference to a grid square of one metre gives a building, and the households and people in it, a unique geographical location. Data with such references can be captured and aggregated for any area with a boundary represented by a line of co-ordinates - termed a digital boundary.

Every record on the output database of the 2001 Census has a co-ordinate reference to a one metre resolution, as well as a postcode and more conventional area codes. This implements the NISRA geographical referencing strategy and allows the data to be aggregated to higher geographies. Requests for statistical aggregations to alternative geographical units will be subject to disclosure control considerations.

Output areas

The 2001 Census Output Areas are designed specifically for statistical purposes. They are based on the results of the 2001 Census and will be used not only for Census output but also for Northern Ireland Neighbourhood Statistics. The system for creating Output Areas is fully automated and applies systematic and consistent criteria throughout  Northern Ireland. Its development has been made possible through the availability of the computing power necessary to facilitate the automatic zoning methods used. In simple terms, the system creates Output Areas with around 125 households. The system achieves this by examining unit postcode polygons and, using iterative techniques, then looks to aggregate contiguous postcodes within each Ward to optimise the homogeneity criteria for Output Areas.  All Output Areas produced are larger than the confidentiality threshold of 40 households and 100 persons.  The physical size of Output Areas varies greatly and is dependent on their location.  They have regular shapes and, where possible,  follow existing features(ie roads, rivers, fencelines etc.). They nest within Wards and comprise of whole unit postcodes and part postcodes.  

Reports

Each Census report will drill down to a specifc geographic level.

Key Statistics  - around 500 counts covering all main Census topics, designed as indicators to be presented as percentages in a limited number of simple tables. [Output Area]

Census Area Statistics (CAS) - around 6,700 counts generally presented as cross-tabulations, but also including the simple univariate tables, covering all main Census topics and the relationships between them. [Output Area]

Standard Tables  - around 25,000 counts generally presented in cross-tabulations giving more depth than the CAS, including additional topic extension tables for larger populations. [Ward]

Origin/destination  - figures on the people with workplaces in an area and on out-migrants are included in the Standard Tables and CAS, but the flows of workers and migrants between areas are provided in additional matrices. [Output Area]