Geography Markup Language (GML) is an XML grammar defined by the Open Geospatial Consortium (OGC) used to express geographical features. It serves as a standard for the transport and storage of geographic information, including both the geometry and properties of geographic features. GML allows for the representation of various geographic objects, such as points, lines, polygons, and more complex features like roads, rivers, and buildings. It is designed to be highly flexible and extensible, allowing users to define their own feature types and attributes. GML is widely used in geographic information systems (GIS), web mapping applications, and other geospatial data exchange scenarios. Its XML-based structure makes it easily parsable and interoperable across different platforms and software. The complexity of GML can vary depending on the specific application, ranging from simple representations of geographic features to highly detailed and complex models.