[Boost-users] [BGL] how to build a hierarchy of graphs

Hi, I need to build a hierarchy of graphs bottom up. Conceptually, every level(>1) of graph is a result of merging groups of nearest neighbors of its immediate lower level, according to some sort of criteria. My general question is, what is the best way of building this hierarchy using BGL?(or, BGL already has this kind of mechanism somewhere?) (I didnot read in detail concepts like subgraph, filter, etc. From the names, they seems to of help?) And Is it possible to effeciently retrieve information both within same level and across levels? Thanks in advance. Shufei