Taking OSM – a collaborative project of map production – as a case, and following the academic tradition of critical cartography, this article applies the two theoretical perspectives of “communicative figuration” and “community of practice” to the empirical data collected from the OSM community in China by means of virtual ethnography and qualitative interview, in order to reveal the role of the media in the production of map knowledge. It is found that a media ensemble is formed around the production of map knowledge in the OSM community, including three different layers, i.e., the core, communicative, and compensational cartographic layers. In them, cartographers carry out different media practices: mapping based on the iD editor and GPS devices, negotiating among cartographers within and outside OSM, and developing technical patches and appropriating other technologies outside OSM. In the process of participatory mapmaking, the seemingly democratic activity is actually the product of the interplay of individual experiences, local knowledge, community norms, scientific discourse, state power, identity, and media ensemble. Finally, the article attempts to combine the mediatization theory with empirical research, using “media ensemble” as a thread to link various media practices, in the hope of drawing the picture of the communicative figuration around the production of map knowledge.