As our urban environments are densifying, it is essential to extend traditional cadastral systems that are based on two dimensional representation of ownership to support 3D. With the need to define property ownership in vertical as well as horizontal dimensions becoming pertinent around the world, a practical solution to represent 3D cadastral data is needed. The Land Administration Domain Model (LADM, ISO 19152) already covers such situations since the spatial unit defined in the Spatial Unit package in LADM can refer to a single volume of space (or multiple volumes of space) besides 2D representations. LADM is a conceptual model that allows land administration objects and relationships to be described. The power of the model is the ability to describe different cadastral systems in different countries or regions in a consistent way. CityGML is an information model and data exchange standard for 3D city model data. It does not contain specifics about land administration. The paper examines how the LADM conceptual model, the representation of legal spaces in particular, can be mapped to and encoded as a CityGML Application Domain Extension (ADE). The CityGML ADE implements a data exchange format but the underlying model could also be used as a starting point to create a database schema for data storage. The paper addresses the modelling issue of integrating different information models that define or refer to the same or overlapping concepts. The possibility to achieve greater integration between ISO19152 and CityGML by including each others concepts in future versions is also discussed. Relating legal features to physical features, a common occurance in practice, is addressed from a data modelling perspective. The paper is intended to stimulate discussion about the topic as well as further development.