Geography Markup Language

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Geography Markup Language, GML short, is a markup language for the exchange of spatial objects ( "features" ). GML is an application of XML and schema descriptions ( XML schema files *. Xsd ) set. GML allows the transmission of objects with attributes, relations and geometries in the field of spatial data to include non -conventional data such as sensor data.

GML is by the Open Geospatial Consortium ( OGC), established jointly with the ISO TC 211, the ISO technical committee of establishing digital geobezogener data. Meanwhile, GML is available in version 3.2.1. Like all the results of the OGC process is the documentation freely available for everyone.

Conformity to standards

With GML version 3.2 is now also on the International Standards of ISO 191xx - recycled series. The OGC Specification for GML 3.2 is identical to ISO 19136 and thus even an official International Standard ISO. GML taken into account so that above all the stipulations on spatial reference basic forms in ISO 19107th

The GML model

Originally based GML model on the Resource Description Framework (RDF) of the World Wide Web Consortium (W3C). Later, the OGC introduced XML schemas in GML to facilitate the linking of many different relational databases with spatial data. The resulting XML schema-based GML retains many RDF elements, including the concept of inheritance of properties of the parent object and the use of references to non - local features (remote property references ).

GML has a rich set of primitives that are used to build application-specific schemas or application languages ​​. The primitives include:

  • Object ( feature )
  • Geometry (geometry )
  • Coordinate reference system ( coordinate reference system )
  • Time (time)
  • Dynamic object (dynamic object)
  • Coverage with the inclusion of geographical maps ( coverage )
  • Unit (unit of measure )
  • Design rules for the map display (map presentation styling rules)


GML profiles are both expressed logical limitations of GML and can through a document, an XML schema or. These profiles are used to facilitate the introduction of the GML standards. The following profiles have been published or proposed for general use:

  • A point profile ( profile point ) with point geometric data without assuming full GML grammar
  • A simple object profile for GML (GML simple feature profile ) that supports the query and the treatment of vector objects, eg via Web Feature Services (WFS )
  • A GML Profile for JPEG 2000 (GML in JPEG 2000, GMLJP2 )
  • A GML profile for RSS ( GeoRSS GML)

Profiles in GML are no application schemas (application schema ): while profiles are element of the GML namespace and describe limited subsets of GML, are regimens of XML vocabularies for the application of GML and are located in the target namespace that is specified by the application. Application schemas can use the full amount of the GML schemas or specific GML profiles. Profiles are often defined to implement GML -based languages ​​for particular uses, such as for aviation, nautical mapping or natural resource management.

Since version 3 of GML two XSLT scripts are included (usually as subsets tool " subset tool ") that will help GML profiles can be constructed.

Application schemas

Application schemas are the appropriate representation geobezogener data for a particular application area using GML. This schema describes the object types whose data presented and to be processed by the application.

GML geometries

GML encoded GML geometries (GML geometries, or geometric characteristics ) of geographic objects as elements within GML documents. The geometries of the objects can describe such things as roads, rivers or bridges.

The most important object types in GML 1.0 and 2.0 are

  • Point
  • LineString
  • Polygon

This model is identical to the KML.


GML is an XML standards for the GeoWeb infrastructure, with the help of Internet-enabled devices receive access to geobezogene data, such as Traffic conditions and the location of stores. GML is also used in the standard -based exchange interface (NAS).


KML stands for Keyhole Markup Language and is distributed through Google world. GML is able to open up the content geobezogener documents by ( such as bridges, roads, buoys and vehicles) describes a spectrum of application objects and their properties. KML is, however, for the visualization of geographic information, and can be used to represent GML content. On the other hand, GML be extended so that it can display content in the form of KML.