Geography Markup Language
A vector map, with points, polylines and polygons.
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| Filename extension | .gml or .xml |
|---|---|
| Internet media type | application/gml+xml |
| Developed by | Open Geospatial Consortium |
| Initial release | 2000 |
| Latest release |
3.2.1
(27 August 2007) |
| Type of format | Geographic Information System |
| Extended from | XML |
| Standard | ISO 19136:2007 |
The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) 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. Key to GML's utility is its ability to integrate all forms of geographic information, including not only conventional "vector" or discrete objects, but coverages (see also GMLJP2) and sensor data.
GML contains a rich set of primitives which are used to build application specific schemas or application languages. These primitives include:
The original GML model was based on the World Wide Web Consortium's Resource Description Framework (RDF). Subsequently, the OGC introduced XML schemas into GML's structure to help connect the various existing geographic databases, whose relational structure XML schemas more easily define. The resulting XML-schema-based GML retains many features of RDF, including the idea of child elements as properties of the parent object (RDFS) and the use of remote property references.
GML profiles are logical restrictions to GML, and may be expressed by a document, an XML schema or both. These profiles are intended to simplify adoption of GML, to facilitate rapid adoption of the standard. The following profiles, as defined by the GML specification, have been published or proposed for public use:
Note that Profiles are distinct from application schemas. Profiles are part of GML namespaces (Open GIS GML) and define restricted subsets of GML. Application schemas are XML vocabularies defined using GML and which live in an application-defined target namespace. Application schemas can be built on specific GML profiles or use the full GML schema set.
Profiles are often created in support for GML derived languages (see application schemas) created in support of particular application domains such as commercial aviation, nautical charting or resource exploitation.
The GML Specification (Since GML v3.) contains a pair of XSLT scripts (usually referred to as the "subset tool") that can be used to construct GML profiles.
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