This paper foregrounds the methodological question of how the heuristic research practices of mapping and ethnography operate together to co-produce situated knowledge of/with the urban margin. By critically reflecting on collaborative map-making with young adults in Dharavi (Mumbai), it argues for mapping as an open-ended collaboration in which mappers’ various ‘finding’ and ‘founding’ acts to support the production of situated knowledge of an ever-shifting urban margin. The continuous efforts to make such knowledge visible is through re-reading, re-writing and re-drawing acts. The method prompted by this experience is proposed as ‘popular cartography’. It aims to transcend mappers’ backgrounds, technical skills, and disciplinary biases, and offers a collaborative medium for expressing often overlooked, opaque or difficult-to-describe lived experiences.