queen contiguity as soon as the first neighbour point is found within
snap distance (if not identical, which is tested first); a second
neighbour point indicates rook contiguities. For details of alternatives
for spherical geometries, see section @ref(spher-poly2nb) below.</p>
</div>
<div class="section level4">
<h4 id="contiguity-neighbours-from-invalid-polygons">Contiguity neighbours from invalid polygons<a class="anchor" aria-label="anchor" href="#contiguity-neighbours-from-invalid-polygons"></a>
</h4>
<