Geography Markup Language (GML) is an XML grammar defined by the Open Geospatial Consortium (OGC) used to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. It provides a variety of object types for representing geographic features, including points, lines, polygons, rasters, and coverages. GML is widely used in geographic information systems (GIS) and location-based services (LBS) for storing, transporting, and processing geographic data. It allows for the encoding of both geometric and non-geometric properties of geographic features, enabling interoperability between different GIS platforms and applications. GML is designed to be extensible, allowing users to define their own application-specific schemas and feature types. It supports complex geometries, coordinate reference systems, and metadata, making it a powerful tool for representing and exchanging geographic information.