he <tt class="docutils literal"><span class="pre">name</span></tt> field contains the name of each city, so
we use the <tt class="docutils literal"><span class="pre">member</span></tt> function object from the <a class="reference external" href="http://www.boost.org/libs/multi_index/doc/index.html">Boost.MultiIndex</a>
library to extract the name, e.g.,</p>
<pre class="literal-block">
namespace boost { namespace graph {

template&lt;&gt;
struct internal_vertex_name&lt;City&gt;
{
  typedef multi_index::membe