On the analysis of immigrant settlement patterns using quadrat counts. The case of the city of Catania (Italy)

Demographers and other social scientists are often interested in characterizing the forces underlying the settlement process of a population within a region of space. Frequently, the only information readily available are on the spatial distribution of individuals in the region, so researchers often try to obtain indications on the nature of the settlement process from the observation of spatial patterns. Such indications are often based on measures of deviation of the observed pattern from complete spatial randomness (CSR). Nevertheless, in this context, CSR is of little interest because of the background geographical variation in the residential capacity within the study area and, typically, researchers are most concerned in clustering above and beyond that due to such geographic variations. Our contribution introduces a descriptive index based on an inhomogeneous Poisson process; under the constant risk hypothesis, every quadrat has an expected number of individuals proportional to its share of the city’s potential residential capacity. This allows to interpret the observed pattern with respect to the urban fabric of the city. An application comparing the settlement patterns of different groups of foreign residents within the urban area of Catania (Italy) is presented.