Public participation geographic information science (PPGIS) has been presented as an alternative to the technocratic methods and tools of GIS. It draws on the generative knowledge practices which emerge when people are clustered together in relation to a decisionmaking practice by intentionally taking part in spatial activities related to the decision. This is a wide context, under which it is important for PPGIS practitioners to reflect on the concepts of “public” and “participation”, adapting their theoretical and practical frameworks to suit the goals and aims of each project. Instead of assuming that including publics will always lead to better quality and more just or democratic outcomes, researchers are encouraged to reflect on the broader geographic and political strategies of involving publics in their work, paying particular attention to building trust and acceptance of PPGIS amongst affected populations. Key to successful participatory GIS is a recognition that whilst everyone is expert in their own lives, conventional practices – including but not limited to those within the spatial sciences – have historically served to privilege specific types of knowledge claim at the expense of others, subjugating the kinds of experiential accounts of place and matter which high-quality PPGIS is able to generate.