Research on generalisation algorithms mainly focused on the most prominent themes of a topographic map, namely roads, buildings, hydrography, terrain and land use. Now that many efficient algorithms exist for such prominent themes (Stanislawski et al. 2014), minor themes like ditches (Savino et al. 2011) or swamp patches (Anderson - Tarver et al. 2011) gain interest from the research community. In OpenStreetMap (OSM), the loose specifications resulted in a large range of unusual themes, e.g. electric lines (Figure 1c), and generalising maps out of OSM data requires to handle such unusual themes. Moreover, another particularity of OSM is the very high level of detail that can be found for some features, compared to traditional geographical databases, e.g. airports, port sites (Figure 1a) or parks (Figure 1b). The unusual details contained in such areas also require specific algorithms to preserve the structure and the relations between the components. Generalising OSM data is a challenging task (Sester et al. 2014) but this paper only focuses on the generalisation of those map themes or areas exhibited in OSM.