Hi, I use an additional map as a graph property. The manual says get_property returns a reference: template const typename graph_property::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