When a geological reserve is split into reserve units, the subdivision is usually performed hierarchically. An open cut coal deposit, for example, could be subdivided into pits, with each pit subdivided into strips and each strip subdivided into cuts. The order of these subdivisions represents the hierarchy. An example of such a coal deposit is shown below.

The hierarchical subdivision of this open cut coal mine can also be represented diagrammatically, as shown below. Each successive subdivision of the deposit is represented by a horizontal layer in the diagram, and they are termed database levels in XPAC.

In XPAC, a Windows style tree diagram is used, similar to the directory tree in Windows Explorer. It is called the structure tree and forms part of each database window. Individual branches in the tree can be expanded and collapsed, allowing unnecessary levels of detail to be hidden. An example of the structure tree for the open cut coal mine is shown below.

Every database will have a record or multiple records automatically created at the top level. This is called Level 0. Up to 10 additional levels can be defined, although it is unusual to require more than about six. Before these levels can be used they must be defined, either when the database is first created or when the structure of an existing project requires modification.

The levels defined in the current database are displayed in the level tree of each database window, an example of which is shown below.

Each database level that is defined has the following properties: