public function area(NeighborhoodBoundary $np)
{
$sql = "SELECT ST_Area(polygon) AS area FROM neighborhood_polygon np WHERE np.id = :np_id";
$rsm = new ResultSetMapping();
$rsm->addScalarResult('area', 'area');
$query = $this->em->createNativeQuery($sql, $rsm);
$result = $query->setParameter('np_id', $np->getId())->getSingleResult();
return $result['area'];
}
