The London boroughs have populations of around 150,000 to 300,000. Inner London boroughs tend to be smaller, in both population and area, and more densely populated than Outer London boroughs. The London boroughs were created by combining groups of former local government units. A review undertaken between 1987 and 1992 led to a number of relatively small alterations in borough boundaries. London borough councils provide the majority of local government services (schools, waste management, social services, libraries), in contrast to the strategic Greater London Authority, which has limited authority over all of Greater London.