Help on Database Design

I would like to design some tables for offices. In the scenario, there are so many offices which are categorized by different levels. Eg. National level, State level, District level etc... The design must satisfy the future need of adding another intermediate level (say, Zone level in between National and State), without any redesign of database. So how could I materialze this?In one table you can create a column with CHAR(5) that specifies the category of level that can be used as a master table to specify these categories with a future addition of sections.