GML

GML (Geography Markup Language) is an OGC XML-based standard for modeling, storing, and exchanging geographic data. It is widely used in professional GIS environments, in WFS services, and in the INSPIRE directive. GML supports complex schemas, coordinate transformations, and rich metadata.

The structure of GML is hierarchical: features are described with geometries (Point, LineString, Polygon, etc.), references to other features, and attributes. Multiple coordinate reference systems are supported via explicit CRS definitions. GML can represent both simple and highly detailed models, making it suitable for cadastre, networks, and 3D.

GML is often used where interoperability and standardization matter, for example for government data, INSPIRE datasets, and exchange between different GIS packages. WFS 1.1 and 2.0 can deliver GML as the default output. The format is less suitable for direct display in simple web clients because of the size and complexity of XML.

In the Dutch context, GML is used for BGT, BAG, and other base registries distributed via PDOK and the Nationaal Georegister. For web maps, GML is often converted server-side to GeoJSON or other lighter formats.