Analysing the spatial scale of population concentrations by religion in Northern Ireland using global and local variograms

The spatial structure of population subgroups is important for many reasons. Information on the spatial concentrations of people in particular groups may be used for guiding government policy and is central to understanding issues such as differential access to resources. In addition, any geographical analysis of populations is partly a function of the spatial scale of variation of subgroups of the population. This article applies variograms to characterise spatial variation in the population of Northern Ireland. The specific interest in this context is the division of the majority of the population of the region into two major groups - those people whose religion is Catholic or Protestant, and the case study presented contributes to previous research on residential segregation by religion. In 2001, the population was more spatially concentrated by community background ('religion or religion brought up in') than by housing tenure, employment or any of a range of other socio-economic and demographic characteristics. In this article, previous analyses are expanded to account explicitly for the spatial scale of variation in the population by religion across Northern Ireland using census data for 1971, 1991 and 2001. The primary focus of the analysis is on the use of global and local variograms to explore spatial variation in the religion variable which is expressed as percentages or as logratios. Local variograms are a novel means of summarising the spatial scale of population concentrations locally, and this article is the first to use them in this way. The analysis contributes to an enhanced understanding of the spatial distribution of the population of Northern Ireland by religion. The analytical framework presented offers a powerful means of capturing information which is likely to be important in a range of contexts from assessing residential segregation to generating population grids.