Abstract
Three potential determinants of urban efficiency, size (geographical spread), sprawl (the location of jobs and homes in the city) and speed (of movement of people and goods), are considered with reference to studies of Paris, London and other cities. Efficiency is defined as labour productivity. It is suggested that there is a city size for which the difference between benefits and costs is maximal and that the available labour market in a large city is only a subset of its total labour market, depending on the transport efficiency and land use patterns (sprawl). The elasticities defining these relationships are modelled.