Coastal seas are important for human societies with many and diverse activities. These space and resource consuming activities exert an increasing pressure on the environment and sometimes result in conflicting interactions. Understanding these interactions remains a challenge for research and civil society. A methodology is proposed to describe the spatio-temporal distribution of several activities in coastal seas. An application is developed in the Bay of Brest (Brittany, France). Spatial, temporal, quantitative and qualitative data acquisition combines analysis of spatio-temporal databases and results from interviews. The heterogeneous data collected are stored in a spatiotemporal database (STDB). Firstly, the STDB is used with a GIS to produce temporal snapshots of daily human activity patterns over a one-year period. Secondly, using the STBD we can identify, quantify and map potential uses conflicts in space and time between activities in the Bay of Brest.