Hello, Are the code and the documentation of the identity_property_map in sync. The documentation says that the class identity_property_map has a template member function operator[](T t) that for any type T, just returns t. In the .hpp file though I find //========================================================================= // A property map that applies the identity function to integers struct identity_property_map : public boost::put_get_helper<std::size_t, identity_property_map> { typedef std::size_t key_type; typedef std::size_t value_type; typedef std::size_t reference; typedef boost::readable_property_map_tag category; inline value_type operator[](const key_type& v) const { return v; } }; Best regards, andreas