SourceFeature processRelationPass2(OsmElement.Relation rel, NodeLocationProvider nodeLocations) {
    // Relation info gets used during way processing, except multipolygons which we have to process after we've
    // stored all the node IDs for each way.
    if (isMultipolygon(rel)) {
      List<RelationMember<OsmRelationInfo>> parentRelations = getRelationMembershipForWay(rel.id());
      return new MultipolygonSourceFeature(rel, nodeLocations, parentRelations);
    } else {
      return null;
    }
  }
Estimates the resource requirements for a multipolygon geometry multimap for a given OSM input file.
planetiler-core/src/main/java/com/onthegomap/planetiler/reader/osm/OsmReader.java