Maritime Spatial Planning (MSP) is an effective tool for conciliating human activities and environmental values, building on spatial data and geoinformation technologies. However, socio-economic information is distinctly underrepresented in the rapidly growing supply of spatial information. The spatial distribution of current and future activities and opinions has traditionally been the silent information of scientists, local actors and the public. Moreover, future projections and policies exist in qualitative, non-spatial formats, incompatible with quantitative biophysical spatial data layers. This article aims at promoting the generation and application of spatial socio-economic information for the purposes of MSP. We examine one workflow of converting the socio-economic knowledge of individual experts to spatial data, and further to refined spatial knowledge. We illustrate how participatory mapping, data interpretation and core geocomputing methods may be used to generate data, and discuss the main issues related to their generation and use. The results suggest that participatory mapping can provide valuable data for the MSP process, helping in filling the gap of missing socio-economic information. The process is highly subjective: the presentation of background information, the framing of the questions and the interpretation of the spatial data may have notable influence on the generated information. Furthermore, both the technology of the data collection and applied analysis methods have distinct effects on spatial information and its validity.