The user may define as many topology layers as is necessary to support their application. A feature may participate in more than one layer. Typically this should be a “top down” hierarchy and not a “circular” one.

For example:

Parcel layer consists of: parcel boundary, parcel node, parcel area, subdivision node, and subdivision boundary.

Subdivision layer consists of: subdivision node, subdivision boundary, and subdivision area. This layer should not contain any “parcel” items as that may lead to undesirable edge duplication and may, logically, render both layers identical.