Data Preparation has become another challenge to the many existing ones in mask making. This was mainly brought about by the advent of OPC and PSM layouts. The amount of data, doubling every year, has experienced a quantum leap. The more aggressive optical proximity correction the greater the leap. Hierarchical data treatment is one of the most powerful means to keep memory and CPU consumption in reasonable ranges. Only recently, however, has this technique acquired more public attention. In this paper we will present means to quantitatively measure the degree of hierarchy. In addition to global numbers local numbers turn out to be extremely helpful. They may serve the purpose to treat different branches of a tree, e.g. of a memory layout, by different approaches. Several alternatives exist, which have, to date, not been thoroughly investigated. One is a bottom-up attempt to treat cells starting with the most elementary cells. The other one is a top-down approach which lends itself to creating a new hierarchy tree. A trivial approach, widely used so far, is to flatten the layout. Conditions will be shown for the alternatives to work most effectively.