The document describes a project to harmonize spatial base data across the border between Saxony, Germany and the Czech Republic. The project aimed to make the data interoperable by establishing a common coordinate reference system, integrating a shared border geometry, and developing semantic mapping functions between the two countries' data models (ATKIS and ZABAGED). Through geometric and semantic harmonization methods, the project resulted in connected cross-border geospatial data that can be interpreted using either data model.