Before revision:  Finally, we give an algorithm for assigning nodes to zoom levels that minimizes the  number of nodes appearing while the user zooms in to a lower level. Keeping the number of such nodes low helps avoiding abrupt changes when zooming in and out between the levels  .
After revision:  Finally, we give an algorithm for assigning nodes to zoom levels that minimizes the number of nodes appearing while the user zooms in and out between the levels .