A situation map that shows the overview of a disaster situation serves as a valuable tool for disaster response teams. It helps them to orientate their location and to make disaster response decisions. It is, however, a complicated task to rapidly generate a complete and comprehensive situation map of a disaster area, particularly due to the centralized organization of disaster management and the limited emergency services. In this study, we propose to let the affected population be utilised as an additional resource that can actively help to make such a situation map. The aim of this study was to investigate the possibility of constructing a shared situation map using a collaborative distributed mechanism. By examining earlier research, a detailed list of potential problems is identified in the collaborative map-making process. These problems were then addressed in an experiment which evaluated a number of proposed solutions. The results showed that more collaboration channels led to a situation map of better quality, and that including confidence information for objects and events in the map helped the discussion process during the map-making.