Geography Markup Language

Geography Markup Language
Name	Geography Markup Language
Abbreviation	GML
Developer	Open Geospatial Consortium
Initial release	2001
Latest release	2012 (GML 3.2.1)
Website	Open Geospatial Consortium

Geography Markup Language is an XML grammar that models, encodes, and transports geographic information for interoperability across systems. Designed by the Open Geospatial Consortium and used in conjunction with standards from the International Organization for Standardization, European Committee for Standardization, and national mapping agencies, it supports exchange of feature collections, coordinate reference systems, and geometry encodings. GML is integral to implementations by institutions such as the United States Geological Survey, European Space Agency, NASA, and national cadastral authorities.

Overview

GML provides a platform-neutral syntax for geographic features rooted in technologies and institutions like Extensible Markup Language, World Wide Web Consortium, Simple Object Access Protocol, Geographic Information Systems, and ISO 19107 spatial schemas. Implementers from organizations such as Esri, Oracle Corporation, Microsoft, Google, and Apache Software Foundation leverage GML for data interchange alongside standards from OGC Web Feature Service, OGC Web Coverage Service, INSPIRE, and national frameworks like National Spatial Data Infrastructure. GML's role spans producers and consumers including the United Nations, European Commission, National Aeronautics and Space Administration, and municipal authorities like the City of New York.

History and Development

Development of GML began under the auspices of the Open Geospatial Consortium with contributions from stakeholders including Ordnance Survey, United States Geological Survey, Canadian Geospatial Data Infrastructure, and vendors such as Intergraph and Bentley Systems. Early versions aligned with ISO standards like ISO 19136 and drew on modeling work from bodies such as ISO/TC 211 and projects like INSPIRE Directive and Global Spatial Data Infrastructure. Key milestones involved collaborations with research agencies including Centre National d'Études Spatiales, Jet Propulsion Laboratory, and academic groups at Massachusetts Institute of Technology, University of Cambridge, and ETH Zurich.

Technical Specification

GML's technical basis references schemas and standards developed by ISO/TC 211, World Geodetic System 1984, and coordinate reference frameworks like EPSG Geodetic Parameter Dataset. The specification defines elements for geometry types used by agencies like National Oceanic and Atmospheric Administration, descriptions compatible with ISO 19115 metadata, and application schemas employed by the European Environment Agency and United States Census Bureau. GML integrates XML Schema constructs from the World Wide Web Consortium and uses namespaces and schema locations familiar to OASIS and W3C implementations.

Encoding and Data Models

GML encodes primitives such as Point, LineString, and Polygon in XML, aligning with feature and geometry models used by institutions like Natural Resources Canada, Australian Bureau of Meteorology, and German Federal Agency for Cartography and Geodesy. Application schemas map to organizational data models employed by Ordnance Survey topographic datasets, USGS National Hydrography Dataset, and cadastral records from agencies like Land Registry (England and Wales). Coordinate reference systems and transformations reference resources such as EPSG, NAD83, and European Terrestrial Reference System 1989, enabling integration with services like OGC Web Map Service and OGC Catalogue Service.

Use Cases and Applications

GML is used in web mapping and catalogue services at entities like United Nations Environment Programme, World Bank, and city authorities including City of London for land registry, urban planning, and disaster response by organizations such as Red Cross and World Health Organization. Remote sensing workflows at European Space Agency and NASA Earth Science programs use GML to describe footprints and metadata, while utilities such as Enel, National Grid (Great Britain), and transportation agencies like Deutsche Bahn and Transport for London employ GML for network models. Environmental modelling projects at Intergovernmental Panel on Climate Change, Food and Agriculture Organization, and research centers like Scripps Institution of Oceanography also adopt GML-based exchange.

Implementations and Software

Software that reads or writes GML includes commercial systems such as Esri ArcGIS, Safe Software FME, and Oracle Spatial as well as open-source projects like GeoServer, MapServer, GDAL/OGR, PostGIS, and the Apache SIS project. Client libraries and toolkits appear in platforms maintained by Microsoft, Google, and independent communities including OpenStreetMap contributors, while desktop GIS applications from QGIS and enterprise solutions from SUSE and Red Hat integrate GML workflows for ingestion, validation, and transformation.

Interoperability and Standards Integration

GML is positioned within an ecosystem that includes the OGC Web Feature Service, OGC Sensor Observation Service, ISO 19115, and directives like INSPIRE Directive to ensure interoperability across agencies such as European Commission, USGS, and Japan Aerospace Exploration Agency. Conformance testing and profiles reference initiatives like CEN standards, validation tools from OGC Compliance Program, and harmonization efforts involving UN-GGIM and regional bodies such as EuroGeographics. Integration with catalogue services, metadata registries, and geoprocessing chains enables coordinated exchanges between institutions including World Bank, United Nations Educational, Scientific and Cultural Organization, and national ministries.

Category:Geographic information systems