Although branded as ‘obstructionists’ and major agents of ‘disease and filth’ by city authorities, food vendors remain the pivotal node in the local food system in most informal settlements; therefore, their interaction with the environment and infrastructure services, and challenges they face to keep the food safe to eat, requires further grounded exploration. Food vendors from informal settlements in Nairobi, Kenya, who are acting as mappers and change agents, are building multi-layered views of places through the deliberative process of knowledge coproduction by participatory sensing, which lead to opportunities and challenges to improve those places.