Informal settlements pose great challenges to urban planners, as very often the data available on those locations is insufficient to inform planning decisions. For instance, demographic estimates are often approximate at best, what makes it difficult to dimension the basic services to be provided. At the same time, there is a less material, political perspective behind these extra-legal, self-help processes of housing construction, for it is not only houses that are being auto-constructed in this process, but the very citizenship of those engaged in it: by actively participating to the production of the urban space, those individuals aim to legitimize their claims to be effectively integrated to the “formal” city. The questions raised above seem to be connected to one general issue: the invisibility of a large proportion of the urban population that cannot be found in any official record or in any official map. In order to address this invisibility issue, I present a mapping solution that has been developed over the past years in collaboration with the NGO Teto-Brasil, which proposes, precisely, to bring visibility to the most vulnerable populations in urban areas.