Urban density is often taken to be self-evident and treated as an indicator or attribute of urban space upon which urban planning and individual planning decisions are made. This article makes the case for thinking about density as a relational and social quality produced by identifiable associations, practices and systems of human interactions, specifically with infrastructural technologies. Based on ethnographic research in Mumbai, the paper will consider several different sites at which density operationalizes an incessant sense of temporariness and anticipation within the frame of social relations. These geographies of density yield surprising circumventions of functionality and planning but they also make possible transformation within existing frames of relations. Much of the recent urbanist literature on Mumbai focuses mainly on the slum not only as an empirical but also an analytic geography. Based on the ethnographic work on Mumbai, the article suggests other sites beside the slum for theorizations of the multitude. Doing so might yield new insights into the relationship between built form and urban design as well as accounts of the city that are not trapped either by normative and prescriptive models of the city or by the need to turn to a redemptive reading of chaos and misery.