Measuring local segregation in Northern Ireland Chris Lloyd, Ian Shuttleworth and David McNair School of Geography, Queen’s University, Belfast ICPG, St Andrews, August 11 th -14 th 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) Catholics (43.8%) and 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 b i and w i 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 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 Gaussian function for a 20 km bandwidth

Results for variants of D IndexValue D0.672 D(adj)0.558 D(w)D(w)0.564 D(s)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.