Although there is a vast literature available on interoperability models, and their respective interoperability levels, limited research has been carried out on the development of interoperability models for the implementation of Spatial Data Infrastructures. This article demonstrates the important role of metadata elements in the formalisation of interoperability models for the implementation of Spatial Data Infrastructures. It describes an approach for designing an integrated interoperability model based on the definition of a common template that integrates seven interoperability levels. They are: technical, syntactic, semantic, pragmatic, dynamic, conceptual and organisational levels. A non-hierarchical structure is proposed to ensure the relationship among these interoperability levels.

The evolution of Geographic Information Systems (GIS) has witnessed an important step towards achieving interoperability through the communication, exchange, cooperation and sharing of resources between systems. The main developments in interoperability include the use of standards for transfer and exchange of geographical information, the integration of different data types up to the development of comprehensive interoperability models. This article aims to review the main advances in interoperability of GIS and provide a basis to identify the future research issues in this field. It first considers the various points of view from which interoperability can be defined and then examines the concept of interoperability itself. An overview is provided on how interoperability can be modelled by discussing the main aspects that directly have an effect on how interoperability levels have been created according to different contexts and purposes of use. It also points out the significant advances in terms of measures that can determine the ability of a GIS to interoperate with other systems, predict the resources needed for successful interoperation, and discover techniques useful to achieving interoperability. We conclude with some suggestions where the research will go next.