This chapter analyses how different discourses influence knowledge-building processes in terms of their main concerns, water sector boundaries, and types of information considered legitimate, in the context of Lima. It shows how these processes are embedded in urban configurations, and how the legitimacy of mapping processes needs to be negotiated across boundaries. We analyse how iterative mapping processes within three concertación (Concertación’ has no proper translation into English. We have discussed the concept elsewhere (Miranda and Hordijk 1998). It refers to the process of reaching agreements for joint action through dialogue and deliberation.) processes in Lima reveal uneven geographies of water-related vulnerabilities and inequalities, and presenting the outcomes of the cross-boundary processes of social construction for generating, analysing, and exchanging knowledge on water vulnerabilities. Three research and policy-building projects in Lima reflect how mappings of ‘water-related vulnerabilities and risks’ are socially constructed. Firstly, maps draw on different discourses and framings, data inputs and classifications at multiple spatial scales. Secondly, they visualise spatial inequalities and link multiple dimensions to one geographic locality, building a more integrated understanding of the dynamics and spatial differentiation of Lima’s ‘waterscape’, combining human and natural processes. As a result, it becomes easier to discuss the legitimacy of different types of knowledge among various actors. Thirdly, maps facilitate ‘exchange on priorities, conflicts and synergies’, providing inputs into negotiation processes between actors in water governance configurations. Although mapping produces new types of knowledge, it is necessary to ensure that the results are incorporated into policy-making and implemented for wider acceptance.