The transfer of design data into nature is a necessary task during the construction of a building. For this, the geodetic Coordinate Reference System (CRS) used during the design process needs to be accounted for and the induced distortions handled appropriately. In the context of Building Information Modelling (BIM), the CRS represents the metadata of the initial model which needs to be included and maintained throughout project’s lifetime. When a project’s construction site spans multiple countries, the initial data is available in different national CRSs and transforming them completely free of residuals is impossible. For the Brenner Base Tunnel between Austria and Italy, a new compound CRS was designed, representing a homogeneous reference system for all surveying and construction work. We present its definition and the rationale behind it. We highlight the requirements for BIM models and design systems and present current deficiencies.