The physical environment and social well-being of central cities depend largely on employment opportunities, a rising tax base, and income distribution. Unskilled immigrants are an increasing proportion of the urban population, and the decreasing number of jobs available to them means they rely on government for welfare, medical care, housing, food, and other essentials. At the same time, the ability of central cities to provide these services is hampered by the continuously declining tax base resulting from the suburbanization of industries and the movement of the middle class away from city centres.