While the prevalent view positions data as an objective and unbiased resource of truth about the world, scholars have noted that this understanding cannot be all-encompassing and data activists may comprehend the relationship between knowledge, reality, and data differently. Data activists are civil society actors with a critical stance towards datafication; they either consider data as a political issue or employ it to advance desirable social change. This article investigates activists’ data epistemologies in a twofold manner. First, it poses the question of how activists can simultaneously use a certain dataset while questioning its credibility. Second, the article explores how activists’ data epistemology transforms other domains of socio-political grassroots interventions. To answer these questions, I turn to the case of the DTP Map–an interactive geoweb map of traffic accidents in Russia made by activists using the official governmental data. Turning to the concept of contentious data politics, I demonstrate how the project transforms by continuously dealing with the data’s epistemologically ambiguous nature. In their data practices aimed at gaining and maintaining the users’ trust, activists have tried to ensure their project will be employed by various collectives for the common goal of reducing traffic accidents in Russia. Their data practices can be considered both a repertoire of social change and a stake of activist intervention. Crucially, in the process of map-making, activists do not gain the epistemologically unambiguous view of data but rather they manage to retain this ambiguity and make it a constitutive part of their project.