A model is proposed which explains the spatial distribution of different income groups in terms of the relation between the cost of living in a particular geographic area and the income of its inhabitants. The applicability of this model to spatial inequalities in Israel is investigated, using data from five subsequent censuses of population and housing. The analysis indicates that changes in the spatial variation of various indicators of development do not follow a uniform pattern: the extent of interregional disparity differs with the indicator selected for measuring it. Furthermore, whereas development in the central part of Israel has tended to become more uniform over time, the country's peripheral regions have become more polarized. Several strategies are proposed for reducing the extent of interregional disparities.