GML (Geography Markup Language)

GML is an OGC standard and ISO 19136, in which geographic features are described in plain XML: every feature has its own geometry and set of properties. GML underpins the European INSPIRE infrastructure, WFS service responses and exchange between agency GIS systems — wherever a textual, readable and verifiable format is required.

OpenStreetMap maps are exported to GML when the receiving side works by regulation rather than by convenience: the GIS department accepts XML, the exchange bus validates the document, the corporate system only knows OGC formats. For your own internal work GeoJSON or GeoPackage are handier, while GML is the language of inter-agency conversation.

The output is a single .gml: one wfs:FeatureCollection gathering all the layers of the area. The feature element name repeats the name of the source layer (roads, buildings, water and so on), each feature has its own gml:id, and OSM tags are laid out as child properties. Coordinates are WGS84 (EPSG:4326) with eight decimal places.

The limitations are stated honestly. The document follows the GML 3.2.1 structure with the GML and WFS namespaces, but an application schema (.xsd) of its own is not shipped alongside — conforming to a particular customer schema is done on the receiving side. Each layer is capped at 200,000 features: XML is heavy, and this keeps the file at a workable size.