Abstract This paper presents an account of spatial ontology and explanation that highlights a largely ignored dimension of social spatiality: the opening and occupation of places for activity that automatically occurs whenever there is human life. The first part analyzes this space of places on the basis of Heidegger's account of ongoing life, and uses the resulting analysis to describe the spatiality of social formations. The second part analyzes spatial explanation on the basis of this spatial ontology. It (a) argues that the explanation and explanatory uses in social science of the spatial properties of social phenomena do not differ in principle from the explanation and explanatory uses of other features of social life, and (b) defends two existing versions of socio-spatial dialectics. Attention is given to the nature of explanation, the character of social causality, and the proper types of explanation in social investigation.