It is well known that the broad concept of localisation has two connotations, namely, regional specialisation and industrial concentration. The main purpose of this paper is to introduce an entropy index of overall localisation suitable to conceptualise specialisation and concentration as the two sides of the same medal in a nested geographical perspective. The system of dissimilarity entropy measures is potentially applicable to the assessment of the spatial distribution of several economic phenomena when a twofold geographical level of analysis is considered. In the specific case, the decomposition provides an accurate method to quantify the cross-country divergence in localisation from the agglomeration within countries.