One of the few instruments for the analysis of urban sociospatial differentiation, Social Area Analysis, has been widely discussed and has met theoretical as well as empirical objections. In the actual search for indicators of urban differentiation, this problem gains new significance. A model of differentiation, developped out of the empirical knowledge of classical human ecology, is juxtaposed to the Shevky-Bell-approach. Empirical tests show that the indicators of Social Area Analysis may be substituted by two single variables: land value and rent, without any loss of information. Some areas for the application of urban indicators are discussed. At the end, some arguments for the relevance of the ecological approach in theory construction are presented.