Projections suggest that most of the global growth in population in the next few decades will be in urban centers in Asia and Africa, with most of these additional urban residents likely to be concentrated in slums. There’s a need to study this population to ensure effective policy response to their wide-ranging needs. Recognizing that government documentation of slums is incomplete and unreliable, this paper, published by the International Institute for Environment and Development, argues for a need to employ creative methods to locate and sample these understudied populations. By using satellite image analysis and fieldwork to build a sample of Indian slums, the paper reveals how living conditions vary along a wide-ranging continuum of wellbeing, with different points corresponding to different policy needs. Importantly, it also shows that most variation in conditions is due to differences across rather than within neighborhoods.