The need of measures capable of representing the performance of a territory is often met through the use of indicator systems. Such tools, unlike others such as accounting systems, provide information about economic, socio-demographic and environmental phenomena more quickly; this, jointly with their ease of reading, led to their dramatic development within the field of territorial analysis too. However, this resulted in an overproduction of indicators representative of the various phenomena, to the point that the end user, facing an information overflow, has often difficulty in assessing the aspect of interest. In the presence of complex phenomena, characterised by many dimensions, the problem of indicators’ mass is even greater. Hence the need of aggregate measures (composite indexes) built by synthesis procedures applied to indicators, in order to simplify the evaluation of the phenomenon described by the indicators. Basic and composite indexes are often treated in literature as two alternative ways of providing relevant information on a phenomenon. The goal of this note is rather to illustrate the “information gain” resulting from their combined use. The methodology that achieves this gain is the SEA/TIA procedure included in STeMA (Prezioso, 2006b). The application context is that of spatial territorial analysis, with particular reference to all Italian provinces. For these provinces we intend to assess competitiveness in sustainability as already experienced in the ESPON project 3.3 “Territorial Dimension of the Lisbon-Gothenburg Strategy” (Prezioso, 2006b). “Information gain” is to highlight the possibility of regionalising the possible actions of economic policy in light of the Lisbon-Gothenburg objectives, its effects and impacts on basic indicators, leading to a rereading of such indicators and a redefinition of the composite index to be territorialised, starting from a review of the statistical method used.