Cover Pages Logo SEARCH
Advanced Search
Site Map
CP RSS Channel
Contact Us
Sponsoring CP
About Our Sponsors

Cover Stories
Articles & Papers
Press Releases

XML Query

XML Applications
General Apps
Government Apps
Academic Apps

Technology and Society
Tech Topics
Related Standards

Public Comment on GML Specification

OGC Seeks Input on Next Version of Geography Markup Language (GML)

June 25, 2008. Wayland, MA, USA.

The Open Geospatial Consortium, Inc. (OGC) is inviting the public to offer change requests for consideration by the OGC Technical Committee on a revision of the OpenGIS Geography Markup Language (GML) Encoding Standard. GML defines a data encoding in XML for geographic data and a grammar to express models of such data using XML Schema.

GML has come into wide use since it was first adopted as an OGC standard in 2002. Implementations typically specify GML application schemas. GML is consistent with the OGC's entire open geospatial standards platform. GML is the standard that enables information communities and other standards organizations such as the Internet Engineering Task Force (IETF) and OASIS to insert geospatial components into their standards and be confident that their standards will be compatible with mainstream information infrastructure methods of conveying spatial/temporal information.

The current version of GML was approved last year and is also published as ISO 19136:2007 by the International Organization for Standardization (ISO). The OGC Technical Committee is reviewing the need for changes in the standard and wants to receive suggestions from the wider community.

Change requests should be submitted by September 19, 2008. The OGC template for change requests is available at:

Change requests must be sent to

The OGC is an international consortium of more than 365 companies, government agencies, research organizations, and universities participating in a consensus process to develop publicly available geospatial standards. OpenGIS Standards support interoperable solutions that "geo-enable" the Web, wireless and location-based services, and mainstream IT. OGC Standards empower technology developers to make geospatial information and services accessible and useful with any application that needs to be geospatially enabled. Visit the OGC website at:


Sam Bacharach
Executive Director, Outreach and Community Adoption
Open Geospatial Consortium, Inc
35 Main Street, Suite 5, Wayland, MA 01778 USA
Tel: +1-703-352-3938

Summary: Extracted from the GML v3.2.1 Specification Scope Statement and Introduction

The Geography Markup Language (GML) is an XML encoding in compliance with ISO 19118 for the transport and storage of geographic information modeled according to the conceptual modeling framework used in the ISO 19100 series of International Standards and including both the spatial and non-spatial properties of geographic features.

This International Standard defines the XML Schema syntax, mechanisms, and conventions that:

  • Provide an open, vendor-neutral framework for the description of geospatial application schemas for the transport and storage of geographic information in XML

  • Allow profiles that support proper subsets of GML framework descriptive capabilities

  • Support the description of geospatial application schemas for specialised domains and information communities

  • Enable the creation and maintenance of linked geographic application schemas and datasets

  • Support the storage and transport of application schemas and data sets

  • Increase the ability of organizations to share geographic application schemas and the information they describe

Implementers may decide to store geographic application schemas and information in GML, or they may decide to convert from some other storage format on demand and use GML only for schema and data transport.

Note: If an ISO 19109 conformant application schema described in UML is used as the basis for the storage and transportation of geographic information, this International Standard provides normative rules for the mapping of such an application schema to a GML application schema in XML Schema and as such to an XML encoding for data with a logical structure according to the ISO 19109 conformant application schema.

Geography Markup Language is an XML grammar written in XML Schema for the description of application schemas as well as the transport and storage of geographic information.

The key concepts used by Geography Markup Language (GML) to model the world are drawn from the ISO 19100 series of International Standards and the OpenGIS Abstract Specification.

A feature is an 'abstraction of real world phenomena' (ISO 19101); it is a geographic feature if it is associated with a location relative to the Earth. So a digital representation of the real world may be thought of as a set of features. The state of a feature is defined by a set of properties, where each property may be thought of as a {name, type, value} triple.

The number of properties a feature may have, together with their names and types, is determined by its type definition. Geographic features with geometry are those with properties that may be geometry-valued. A feature collection is a collection of features that may itself be regarded as a feature; as a consequence a feature collection has a feature type and thus may have distinct properties of its own, in addition to the features it contains.

Following ISO 19109, the feature types of an application or application domain is usually captured in an application schema. A GML application schema is specified in XML Schema and can be constructed in two different and alternative ways:

  • by adhering to the rules specified in ISO 19109 for application schemas in UML, and conforming to both the constraints on such schemas and the rules for mapping them to GML application schemas specified in this International Standard

  • by adhering to the rules for GML application schemas specified in this International Standard for creating a GML application schema directly in XML Schema

Both ways are supported by this International Standard. To ensure proper use of the conceptual modelling framework of the ISO 19100 series of International Standards, all application schemas are expected to be modelled in accordance with the General Feature Model as specified in ISO 19109. Within the ISO 19100 series, UML is the preferred language by which to model conceptual schemas.

GML specifies XML encodings, conformant with ISO 19118, of several of the conceptual classes defined in the ISO 19100 series of International Standards and the OpenGIS Abstract Specification.

The aim is to provide a standardized encoding (i.e., a standardized implementation in XML) of types specified in the conceptual models specified by the International Standards listed above. If every application schema were encoded independently and the encoding process included the types from, for example, ISO 19108, then, without unambiguous and completely fixed encoding rules, the XML encodings would be different. Also, since every implementation platform has specific strengths and weaknesses, it is helpful to standardize XML encodings for core geographic information concepts modelled in the ISO 19100 series of International Standards and commonly used in application schemas.

In many cases, the mapping from the conceptual classes is straightforward, while in some cases the mapping is more complex (a detailed description of the mapping is part of this International Standard).

In addition, GML provides XML encodings for additional concepts not yet modelled in the ISO 19100 series of International Standards or the OpenGIS Abstract Specification, for example, dynamic features, simple observations or value objects.

Predefined types of geographic feature in GML include coverages and simple observations...


Prepared by Robin Cover for The XML Cover Pages archive.

Globe Image

Document URI:  —  Legal stuff
Robin Cover, Editor: