def _build_clusters(tile)
      used_ids = []
      clusters = []

      _adapter.in_tile(*tile.children).find_each do |child|
        cluster = _adapter.build_from(tile.depth, child)
        clusters << cluster
        used_ids << child.id
      end

      return [used_ids, clusters]
    end
def _build_clusters(tile)
      used_ids = []
      clusters = []

      _adapter.in_tile(*tile.children).find_each do |child|
        cluster = _adapter.build_from(tile.depth, child)
        clusters << cluster
        used_ids << child.id
      end

      return [used_ids, clusters]
    end
return the record IDs used