GML is the most important standard for the transfer of Geodata as it allows to transfer the schema information as well as the data. Important issues: - Motivation, Importance of a Geography Markup Language - History of GML, Overview 19136 - Geography Markup Language - Relation to spatial schema - Supported features in GML (Topology, 3D ...) - Structure of GNL, profiles, application schemas etc. - Transfer of models and of data - Examples