Hi, I use an additional map as a graph property. The manual says get_property returns a reference: template <class GraphProperties, class GraphPropertyTag> const typename graph_property<adjacency_list, GraphPropertyTag>::type& get_property(const adjacency_list& g, GraphPropertyTag); so I would expect I could simply change the map but and forget about it. This does not work and I have to use set_property after my changes which means I have been working with a copy. Any ideas why this happens? Cheers, Torsten