The Spatial Scale of Residential Segregation in Northern Ireland, 1991–2001

Chris Lloyd1, Ian Shuttleworth1 and David Martin2

1School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, UK

2School of Geography, University of Southampton, UK

4th ICPG, The Chinese University of Hong Kong, 10-13 July 2007

Context

• Residential segregation in Northern Ireland an important issue - close links to territoriality and politics

• Meaning and reliability of results debated

• Problems: the modifiable areal unit problem and residential segregation

• What is the spatial scale of residential segregation?

Objectives

• To assess the degree of change in segregation indices with change in the zones used

• To explore the degree and nature of residential segregation in Northern Ireland

Structure

• Northern Ireland• Community background and religion in Northern

Ireland• Methods• Segregation indices and concentration profiles:

1991 and 2001• The Northern Ireland Census grid square

resource• Segregation indices and concentration profiles:

grid square data for 2001• Summary

Counties and major cities of Northern Ireland

Northern Ireland

Community background and religion

Catholics as a percentage of NI population

• 1971 34%

• 1991 43%

• 2001 47% by religion

• 2001 45% by community background (‘religion or religion brought up in’)

Catholics as a percentage of NI population by community background: 2001 wards

Measures of segregation

Concentration profiles: for example, the concentration profile for Protestants in Northern Ireland can be used to ascertain the proportion of Protestants who live in areas which have a population which is 75% or more Protestant.

Residential segregation: 1991

Zonal systems: 2001 Census counts

• Enumeration districts (EDs)• Electoral wards for 1991• Output Areas (OAs)• Electoral wards for 2001

• 2001 Counts transferred to 1991 EDs and wards by the NI Census Office, computer code developed by the project team run by Census Office staff and results returned to project team

Zones N Mean size Mean pop.EDs 3729 3653159.0 426.5 (91)

OAs 5022 2711913.6 336 (01)

Wards 1991 566 24068250.5 2787.8 (91)

Wards 2001 582 23400735.2 2895.7 (01)

Residential segregation: 2001

(R)

Residential concentration profile for 2001: Catholics by religion (R) and community background (CB) for 1991 EDs, OAs, 1991 wards and 2001 wards.

(CB)

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ED 91 CBOA CBWard 91 CBWard CB

Residential concentration profile for 2001: Protestants by religion (R) and community background (CB) for 1991 EDs, OAs, 1991 wards and 2001 wards.

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Residential segregation: 2001

NI Census Grid square resource

• The grid-square data have been produced as a standard output from every NI Census since 1971.

• These data are unique; a similar dataset was generated from the 1971 GB Census but it was then discontinued.

• These data have been under used because they were stored in an inconvenient and hard-to-access COBOL database held by the NI Census Office.

NI Census Grid square resource

• The databases that were created give univariate population counts for a wide range of census variables for a regular lattice of 1km2 grids throughout NI although only total population and household counts are given for cells which fall below a threshold of 25 individuals or 8 households.

• 1971, 1981, 1991: 1km square cells for all NI, 100m square cells for urban areas

• 2001: 1km and 100m square cells for all NI

Percentage Catholic in 1991

Percentage Catholic 2001

Residential segregation: 2001

Compares to, for example:

D for OAs for religion: 0.692, for CB: 0.672

D for wards for religion: 0.617, for CB: 0.601

Residential segregation: 2001

Geographically weighted segregation indices

• Geographically-weighted variants of:– Index of dissimilarity– Index of isolation

Feitosa, F. F., Câmara, G., Monteiro, A. M. V., Koschitzki, T., Silva, M. P. S. (2007) Global and local spatial indices of urban segregation. International Journal of Geographical Information Science, 21, 299–323.

Spatial scale of residential segregation: 2001

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D_OAE Cath_OAE Prot_OA D_wardE Cath_wardE Prot_ward D_100mE Cath_100mE Prot_100m

Segregation indices against bandwidth for 2001 counts (by community background) over OAs, wards and 100m2 grid cells.

E Cath: Isolation index for Catholics

E Prot:Isolation index for Protestants

Conclusions

• There has been little change in residential segregation in NI between 1991 and 2001

• Use of zonal systems with markedly different sizes has a large effect on segregation index results

• Altering the form of similarly sized zones has a limited effect

• Geographically weighted indices for different bandwidths allow assessment of the spatial scale of residential segregation

Ongoing work

• Other approaches for exploring the spatial scale of residential segregation

• Mapping of local segregation indices

• Assessing degree to which results are generalisable

Acknowledgements

• Richard Elliott and Robert Beatty of the Census Office (part of the Northern Ireland Statistics and Research Agency – NISRA) are thanked for making available the grid square data and the results for 2001 counts on 1991 zones.

• The support of the Economic and Social Research Council (ESRC) is acknowledged in funding, through awards RES-000-22-0271 and RES-000-23-0478, part of the work that made this research possible.