Interoperability of GIS infrastructure or architecture ensures the consistent and uninterrupted usage of data and functionalities across platforms and systems. Components or tools residing on distinct platforms can “talk” to each other without friction. Interoperability is a central characteristic, especially important in distributed systems and architectures. It can be applied to different levels or layers of a system, i.e. infrastructure level, data level, business logic level, etc. For example, standard spatial data formats and protocols are especially relevant for handling GIS data across multiple systems and platforms, regardless of their underlying software architecture. This is particularly important in large-scale, collaborative projects involving various teams using heterogeneous GIS architectures. Most software providers, developers communities and standardisation bodies and committees are striving to make their architectures interoperable in an open manner, so proprietary standards and protocols are a potential hindrance to this initiative.