This paper is based upon the results of two research projects that took place in very dissimilar places and contexts, at different situations in the epidemiological transition process, but lead to some important common conclusions. In both studies, a geo-systemic or socio-spatial classificatory model was first constructed, comprising a series of environmental (independent) variables. Second, this model was used to reveal, measure, and try to explain the health disparities existing in the area under study, as measured by certain health indicators (dependent variables). Two socio-spatial models were constructed. The first used 26 environmental variables, measured in the 78 municipios of Puerto Rico. The dependent variables were mortality rates. The second employed 28 environmental variables, measured in the 32 community health department territories (DSCs) of Québec. The dependent variables were physical and mental health indices. The most significant common conclusion of these studies is that the socio-economic level per se, or its classical principal defining elements (income, education level) are not the main determinants of the observed health disparities. A certain stability in the physical and social environment, the person's sense of understanding of his environment and of control over the course and setting of his own life (what is called ambiocontrol) that is induced by this stability appear to be the most important determinants of health. On the other hand, centrality, complexity and instability of the environment are the most pathogenic characteristics of the milieu.
