Current literature on urban planning explores how to use ICT to support citizen participation. Advances in open data and its possibility to easily represent data on maps, opens up new opportunities to support participation and decision making in urban projects. This article investigates how spatial planners today use data to inform the participatory process. Looking at the par- ticipation process as collaboration between planners and citizens allows us to see the participation process itself as generating data that informs future deci- sions and processes. Based on a case study of a participatory process of an ur- ban renewal project, the article investigates the use of structured and unstruc- tured data for participation. The fieldwork is conducted using ethnographically inspired methods, based on participatory observations, interviews and docu- ment analysis. As a result, the incremental decisions, the resulting process, and the data used in this process are mapped out. Besides the need to accommodate heterogeneous data and to allow for integrated analysis of data specific to the neighborhood under development, the important result is that the participatory process itself generates data that informs the further process and the decisions that are part of it. The paper concludes with design implications for decision support for urban planning. In future research, the intention is to explore these implications in a Participatory Design process.