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In order to understand how the social divisions of residential space in Île-de-France evolved between 1990 and 1999, the problem of measuring discontinuities was tackled. To measure major social change in space, this paper proposes an approach combining smoothing and discriminant analysis.The data used (socio-professional categories from INSEE’s censuses of 1990 and 1999 at the level of each IRIS district) show that the two socially opposed spaces are extremely compact and are becoming even more so as small existing centres merge. Mapping also shows a clear trend towards a reinforcement and linearisation of the discontinuities surrounding the more disadvantaged spaces. Conversely, the discontinuities observed around the edges of the most advantaged spaces followed various patterns between 1990 and 1999.