Measures of optimal centrality: Indicators of city effect and urban overloading

'City-effect' is the peculiar quality of large urban settlements enjoyed by their residents and users. It involves a direct access to special ('superior') urban functions, opportunities and services. This is why it is a very much sought after object of individual and collective aspirations. Large cities concentrate city-effect and often act as powerful magnets in attracting commuters and new residents from surrounding areas, where city-effect is weaker. But when concentration goes beyond a certain threshold, overburdened cities pay for their city-effect in terms of decreasing liveability. Searching for optimal centrality, that is an acceptable trade-off between city effect and decreasing liveability, is among the aims of territorial planning. This paper illustrates a research on the measures of optimal centrality, where social indicators play a key methodological role. It was jointly carried out in four European countries. The indicator-building process is described, and a few points resulting from the study on the operational pre-requisites for harmonising and standardising the proposed measures for territorial policies are also offered for reflection.