a
named vertex does not yet exist. However, one can customize this
behavior by specifying a function object that constructs an instance
of the vertex property (e.g., <tt class="docutils literal"><span class="pre">City</span></tt>) from just the name of the
vertex. This customization occurs via the
<tt class="docutils literal"><span class="pre">internal_vertex_constructor</span></tt> trait. For example, using the
<tt class="docutils literal"><span class="pre">vertex_from_name</span></tt> template (provided w