Measuring local segregation in Northern Ireland

Chris Lloyd, Ian Shuttleworth and David McNair

School of Geography,Queen’s University, Belfast

ICPG, St Andrews, August 11th-14th 2004

Outline of the presentation

• Introduction

• Northern Ireland

• Data

• Methods

– D, D(adj), D(w), D(s), I and D(gw)

• Analysis

• Summary

Introduction:Aims of the research

Segregation measures have been applied in the study of many societies and traditionally such measures have been used to assess the degree of division between social and cultural groups across national or regional areas. The degree of segregation can vary substantially from place to place even within cities.

In this paper, the concern is with religious/political segregation – particularly the proportion of Protestants (often taken as an indicator of Unionism) to Catholics (often taken as an indicator of Nationalism). This paper examines a variety of global measures and also local measures that account for spatial variation in segregation.

Northern Ireland

Counties and major cities

Data

• The data derive from the 2001 Census of Population in Northern Ireland

• The zones used are Output Areas, of which there are 5022 with populations ranging from 109 to 2582 (mean of 336 )

The census includes 1,685,269 people (after adjustment for underenumeration) comprising (by community background) 737398 Catholics (43.8%) and 895375 Protestant/other Christian (including Christian related) (53.1%).

Percentage of Catholics in Northern Ireland Source: 2001 Census of Population

Percentage of Catholics in Belfast

The index of dissimilarity

.5.0 i

ii

W

w

B

bD

bi and wi are counts of population in two groups for areal unit i. These are often referred to as the black and white population counts (Wong et al., 1999). B and W are the total population counts across the whole of the study area.

Other measures used were D(adj), D(w), D(s) (Wong, 2003) and local I (Anselin, 1995)

Geographically weighted D

])/(exp[ 221 adi

.5.0)(

ii

ii

ii

iii

ii

w

w

b

bgwD

The counts are weighted using a Gaussian kernel function which obtains a weight, , for the observation i with:

where d is the Euclidean distance between the location of observation i (in this case, the centroid of a zone) and the centre of the kernel and a is the bandwidth of the kernel. Geographically weighted D is given by:

Geographically weighted D

0.00.10.20.30.40.50.60.70.80.91.0

0 20000 40000 60000 80000 100000

Distance (m)

Wei

gh

t

Gaussian function for a 20 km bandwidth

Results for variants of D

Index Value

D 0.672

D(adj) 0.558

D(w) 0.564

D(s) 0.672

Local Moran’s I

Local Moran’s I for Belfast

D by district

GW D: 1 km bandwidth

GW D: 1 km bandwidth for Belfast

GW D: 5 km bandwidth

GW D: 10 km bandwidth

GW D: 15 km bandwidth

GW D: 20 km bandwidth

Summary

• The use of a geographically weighted version of D indicates

clearly variation in segregation (i) geographically and (ii) with

change in spatial scale of measurement.

• While a geographically weighted approach is still affected by the

MAUP, in that the data are provided as counts over areas, the

approach is not constrained by the need to construct aggregates

of the data over larger areas (e.g., districts or counties) to provide

measures of segregation.

• It is possible to provide a variety of different outputs that indicate

how segregation varies as a function of neighbourhood size (in

this case determined by kernel bandwidth).

References

Anselin, L. (1995) Local Indicators of Spatial Association — LISA. Geographical Analysis, 27, 93–115.

Wong, D. W. S. (2003) Implementing spatial segregation measures in GIS. Computers, Environment and Urban Systems, 27, 53–70.