Geography Markup Language

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.

Geography Markup Language
Simple vector map
A vector map, with points, polylines and polygons.
Filename extension.gml or .xml
Internet media typeapplication/gml+xml[1]
Developed byOpen Geospatial Consortium
Initial release2000
Latest release
3.2.1[2]
(27 August 2007)
Type of formatGeographic Information System
Extended fromXML
StandardISO 19136:2007

GML model

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 defined. 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.

Profile

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:

  • A Point Profile for applications with point geometric data but without the need for the full GML grammar;
  • A GML Simple Features profile supporting vector feature requests and transactions, e.g. with a WFS;
  • A GML profile for GMLJP2 (GML in JPEG 2000);
  • A GML profile for RSS.

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.

GML Simple Features Profile

The GML Simple Features Profile is a more complete profile of GML than the above Point Profile and supports a wide range of vector feature objects, including the following:

  1. A reduced geometry model allowing 0d, 1d and 2d linear geometric objects (all based on linear interpolation) and the corresponding aggregate geometries (gml:MultiPoint, gml:MultiCurve, etc.).
  2. A simplified feature model which can only be one level deep (in the general GML model, arbitrary nesting of features and feature properties is not permitted).
  3. All non-geometric properties must be XML Schema simple types – i.e. cannot contain nested elements.
  4. Remote property value references (xlink:href) just like in the main GML specification.

Since the profile aims to provide a simple entry point, it does not provide support for the following:

  • coverages
  • topology
  • observations
  • value objects (for real time sensor data)
  • dynamic features

Nonetheless it supports a good variety of real world problems.

Subset tool

In addition, the GML specification provides a subset tool to generate GML profiles containing a user-specified list of components. The tool consists of three XSLT scripts. The scripts generate a profile that a developer may extend manually or otherwise enhance through schema restriction. Note that as restrictions of the full GML specification, application schemas that a profile can generate must themselves be valid GML application schemas.

The subset tool can generate profiles for many other reasons as well. Listing the elements and attributes to include in the resultant profile schema and running the tool results in a single profile schema file containing only the user-specified items and all of the element, attribute and type declarations on which the specified items depend. Some Profile schemas created in this manner support other specifications including IHO S-57 and GML in JPEG 2000.

Application schema

In order to expose an application's geographic data with GML, a community or organization creates an XML schema specific to the application domain of interest (the application schema). This schema describes the object types whose data the community is interested in and which community applications must expose. For example, an application for tourism may define object types including monuments, places of interest, museums, road exits, and viewpoints in its application schema. Those object types in turn reference the primitive object types defined in the GML standard.

Some other markup languages for geography use schema constructs, but GML builds on the existing XML schema model instead of creating a new schema language. Application schemas are normally designed using ISO 19103(Geographic information -- Conceptual schema language) [3] conformant UML, and then the GML Application created by following the rules given in Annex E of ISO 19136.

List of public GML Application Schemas

Following is a list of known, publicly accessible GML Application Schemas:

  • AIXM Aeronautical Information eXchange Model ( see http://aixm.aero - Commercial Aviation Related Schema)
  • CAAML - Canadian Avalanche Association Markup Language
  • CityGML - a common information model and GML application schema for virtual 3D city / regional models.[4]
  • Coverages - an interoperable, encoding-neutral information model for the digital representation of spatio-temporally varying phenomena (such as sensor, image, model, and statistics data), based on the abstract model of ISO 19123
  • Climate Science Modelling Language (CSML)[5]
  • Darwin Core GML application schema. An implementation of the Darwin Core schema in GML for sharing biodiversity occurrence data.
  • GeoSciML - from IUGS Commission for Geoscience Information
  • GPML - the GPlates Markup Language, an information model and application schema for plate-tectonics[6]
  • INSPIRE application schemas[7]
  • IWXXM - Aviation weather GML application schema
  • LandGML - a GML implementation equivalent to LandXML
  • NcML/GML - NetCDF-GML[8]
  • Observations and Measurements schema for observation metadata and results
  • OS MasterMap GML[9]
  • SensorML schema for describing instruments and processing chains
  • SoTerML schema for describing Soil and Terrain data
  • TigerGML - US Census[10]
  • Water Quality Data Project from Dept. of Natural Resources, New South Wales
  • WXXM - Weather Information Exchange Model

GML and KML

KML, made popular by Google, complements GML. Whereas GML is a language to encode geographic content for any application, by describing a spectrum of application objects and their properties (e.g. bridges, roads, buoys, vehicles etc.), KML is a language for the visualization of geographic information tailored for Google Earth. KML can be used to render GML content, and GML content can be “styled” using KML for the purposes of presentation. KML is first and foremost a 3D portrayal transport, not a data exchange transport. As a result of this significant difference in purpose, encoding GML content for portrayal using KML results in significant and unrecoverable loss of structure and identity in the resulting KML. Over 90% of GML's structures (such as, to name a few, metadata, coordinate reference systems, horizontal and vertical datums, geometric integrity of circles, ellipses, arcs, etc.) cannot be transformed to KML without loss or non-standard encoding. Similarly, due to KML's design as a portrayal transport, encoding KML content in GML will result in significant loss of KML portrayal structures such as regions, level of detail rules, viewing and animation information, as well as styling information and multiscale representation. The ability to portray placemarks at multiple levels of details distinguishes KML from GML, since portrayal is outside the scope of GML.[11]

GML geometries

GML encodes the GML geometries, or geometric characteristics, of geographic objects as elements within GML documents according to the "vector" model. The geometries of those objects may describe, for example, roads, rivers, and bridges.

The key GML geometry object types in GML 1.0 and GML 2.0, are the following:

  • Point
  • LineString
  • Polygon

GML 3.0 and higher also includes structures to describe "coverage" information, the "raster" model, such as gathered via remote sensors and images, including most satellite data.

Features

GML defines features distinct from geometry objects. A feature is an application object that represents a physical entity, e.g. a building, a river, or a person. A feature may or may not have geometric aspects. A geometry object defines a location or region instead of a physical entity, and hence is different from a feature.

In GML, a feature can have various geometry properties that describe geometric aspects or characteristics of the feature (e.g. the feature's Point or Extent properties). GML also provides the ability for features to share a geometry property with one another by using a remote property reference on the shared geometry property. Remote properties are a general feature of GML borrowed from RDF. An xlink:href attribute on a GML geometry property means that the value of the property is the resource referenced in the link.

For example, a Building feature in a particular GML application schema might have a position given by the primitive GML geometry object type Point. However, the Building is a separate entity from the Point that defines its position. In addition, a feature may have several geometry properties (or none at all), for example an extent and a position.

Coordinates

Coordinates in GML represent the coordinates of geometry objects. Coordinates can be specified by any of the following GML elements:

  • <gml:coordinates>
  • <gml:pos>
  • <gml:posList>

GML has multiple ways to represent coordinates. For example, the <gml:coordinates> element can be used, as follows:

 <gml:Point gml:id="p21" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:coordinates>45.67, 88.56</gml:coordinates>
 </gml:Point>

Note that, when expressed as above, the individual coordinates (e.g. 88.56) are not separately accessible through the XML Document Object Model since the content of the <gml:coordinates> element is just a single string.

To make GML coordinates accessible through the XML DOM, GML 3.0 introduced the <gml:pos> and <gml:posList> elements. (Note that although GML versions 1 and 2 had the <gml:coord> element, it is treated as a defect and is not used.) Using the <gml:pos> element instead of the <gml:coordinates> element, the same point can be represented as follows:

 <gml:Point gml:id="p21" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:pos srsDimension="2">45.67 88.56</gml:pos>
 </gml:Point>

The coordinates of a <gml:LineString> geometry object can be represented with the <gml:coordinates> element:

 <gml:LineString gml:id="p21" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:coordinates>45.67, 88.56 55.56,89.44</gml:coordinates>
 </gml:LineString >

The <gml:posList> element is used to represent a list of coordinate tuples, as required for linear geometries:

 <gml:LineString gml:id="p21" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:posList srsDimension="2">45.67 88.56 55.56 89.44</gml:posList>
 </gml:LineString >

For GML data servers (WFS) and conversion tools that only support GML 1 or GML 2 (i.e. only the <gml:coordinates> element), there is no alternative to <gml:coordinates>. For GML 3 documents and later, however, <gml:pos> and <gml:posList> are preferable to <gml:coordinates>.

For more information on the srsName attribute, see coordinate reference system below.

Coordinate reference system

A coordinate reference system (CRS) determines the geometry of each geometry element in a GML document.

Unlike KML or GeoRSS, GML does not default to a coordinate system when none is provided. Instead, the desired coordinate system must be specified explicitly with a CRS. The elements whose coordinates are interpreted with respect to such a CRS include the following:

  • <gml:coordinates>
  • <gml:pos>
  • <gml:posList>

An srsName attribute attached to a geometry object specifies the object's CRS, as shown in the following example:

 <gml:Point gml:id="p1" srsName="#srs36">
     <gml:coordinates>100,200</gml:coordinates>
 </gml:Point>

The value of the srsName attribute is a Uniform Resource Identifier (URI). It refers to a definition of the CRS that is used to interpret the coordinates in the geometry. The CRS definition may be in a document (i.e. a flat file) or in an online web service. Values of EPSG codes can be resolved by using the CRS Registry Service operated by the Oil and Gas Producers Association (OGP at http://www.epsg-registry.org.

The srsName URI may also be a Uniform Resource Name (URN) for referencing a common CRS definition. The OGC has developed a URN structure and a set specific URNs to encode some common CRS. A URN resolver resolves those URNs to GML CRS definitions.

Examples

Polygons, Points, and LineString objects are encoded in GML 1.0 and 2.0 as follows:

     <gml:Polygon>
         <gml:outerBoundaryIs>
                 <gml:LinearRing>
                         <gml:coordinates>0,0 100,0 100,100 0,100 0,0</gml:coordinates>
                 </gml:LinearRing>
        </gml:outerBoundaryIs>
     </gml:Polygon>
     <gml:Point>
        <gml:coordinates>100,200</gml:coordinates>
     </gml:Point>
     <gml:LineString>
        <gml:coordinates>100,200 150,300</gml:coordinates>
     </gml:LineString>

Note that LineString objects, along with LinearRing objects, assume linear interpolation between the specified points. Also the coordinates of a Polygon have to be closed.

Features using geometries

The following GML example illustrates the distinction between features and geometry objects. The Building feature has several geometry objects, sharing one of them (the Point with identifier p21) with the SurveyMonument feature:

 <abc:Building gml:id="SearsTower">
     <abc:height>52</abc:height>
     <abc:position xlink:type="Simple" xlink:href="#p21"/>
 </abc:Building>
 <abc:SurveyMonument gml:id="g234">
     <abc:position>
         <gml:Point gml:id="p21">
             <gml:posList>100,200</gml:posList>
         </gml:Point>
     </abc:position>
 </abc:SurveyMonument>

Note that the reference is to the shared Point and not to the SurveyMonument, since any feature object can have more than one geometry object property.

Point Profile

The GML Point Profile contains a single GML geometry, namely a <gml:Point> object type. Any XML Schema can use the Point Profile by importing it and referencing the subject <gml:Point> instance:

 <PhotoCollection xmlns="http://www.myphotos.org" xmlns:gml="http://www.opengis.net/gml"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.myphotos.org
      MyGoodPhotos.xsd">
     <items>
         <Item>
             <name>Lynn Valley</name>
             <description>A shot of the falls from the suspension bridge</description>
             <where>North Vancouver</where>
             <position>
                 <gml:Point srsDimension="2" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
                     <gml:pos>49.40 -123.26</gml:pos>
                 </gml:Point>
             </position>
         </Item>
     </items>
 </PhotoCollection>

Note that when using the Point Profile, the only geometry object is the '<gml:Point>' object. The rest of the geography is defined by the photo-collection schema.

History

Initial Work - to OGC Recommendation Paper

Ron Lake started work on GML in the fall of 1998, following earlier work on XML encodings for radio broadcasting. Lake presented his early ideas to an OGC meeting in Atlanta, Georgia, in February 1999, under the title xGML. This introduced the idea of a GeoDOM, and the notion of Geographic Styling Language (GSL) based on XSL. Akifumi Nakai of NTT Data also presented at the same meeting on work partly underway at NTT Data on an XML encoding called G-XML, which was targeted at location–based services.[12] In April 1999, Galdos created the XBed team (with CubeWerx, Oracle Corporation, MapInfo Corporation, NTT Data, Mitsubishi, and Compusult as subcontractors). Xbed was focused on the use of XML for geospatial. This led to the creation of SFXML (Simple Features XML) with input from Galdos, US Census, and NTT Data. Galdos demonstrated an early map style engine pulling data from an Oracle-based "GML" data server (precursor of the WFS) at the first OGC Web Map Test Bed in September 1999. In October 1999, Galdos Systems rewrote the SFXML draft document into a Request for Comment, and changed the name of the language to GML (Geography Markup Language). This document introduced several key ideas that became the foundation of GML, including the 1) Object-Property-Value rule, 2) Remote properties (via rdf:resource), and 3) the decision to use application schemas rather than a set of static schemas. The paper also proposed that the language be based on the Resource Description Framework (RDF) rather than on the DTDs used to that point. These issues, including the use of RDF, were hotly debated within the OGC community during 1999 and 2000, with the result that the final GML Recommendation Paper contained three GML profiles – two based on DTD, and one on RDF – with one of the DTD’s using a static schema approach. This passed as a Recommendation Paper at the OGC in May 2000.[13]

Moving to XML Schema - Version 2.

Even before the passage of the Recommendation Paper at the OGC, Galdos had started work on an XML Schema version of GML, replacing the rdf:resource scheme for remote references with the use of xlink:href, and developing specific patterns (e.g. Barbarians at the Gate) for handling extensions for complex structures like feature collections. Much of the XML Schema design work was done by Mr. Richard Martell of Galdos who served as the document editor and who was mainly responsible for the translation of the basic GML model into an XML Schema. Other important inputs in this time frame came from Simon Cox (CSIRO Australia), Paul Daisey (US Census), David Burggraf (Galdos), and Adrian Cuthbert (Laser-Scan). The US Army Corps of Engineers (particularly Jeff Harrison) were quite supportive of the development of GML. The US Army Corp of Engineers sponsored the “USL Pilot” project, which was very helpful in exploring the utility of linking and styling concepts in the GML specification, with important work being done by Monie (Ionic) and Xia Li (Galdos). The XML Schema specification draft was submitted by Galdos and was approved for public distribution in December 2000. It became a Recommendation Paper in February 2001 and an Adopted Specification in May of the same year. This version (V2.0) eliminated the “profiles” from version 1. and established the key principles, as outlined in the original Galdos submission, as the basis of GML.

GML and G-XML (Japan)

As these events were unfolding, work was continuing in parallel in Japan on G-XML under the auspices of the Japanese Database Promotion Center under the direction of Mr. Shige Kawano. G-XML and GML differed in several important respects. Targeted at LBS applications, G-XML employed many concrete geographic objects (e.g. Mover, POI), while GML provided a very limited concrete set and built more complex objects by the use of application schemas. At this point in time, G-XML was still written using a DTD, while GML had already transitioned to an XML Schema. On the one hand G-XML required the use of many fundamental constructs not at the time in the GML lexicon, including temporality, spatial references by identifiers, objects having histories, and the concept of topology-based styling. GML, on the other hand, offered a limited set of primitives (geometry, feature) and a recipe to construct user defined object (feature) types.

A set of meetings held in Tokyo in January 2001, and involving Ron Lake (Galdos), Richard Martell (Galdos), OGC Staff (Kurt Buehler, David Schell), Mr. Shige Kawano (DPC), Mr. Akifumi Nakai (NTT Data) and Dr. Shimada (Hitachi CRL) led to the signing of an MOU between DPC and OGC by which OGC would endeavour to inject the fundamental elements required to support G-XML into GML, thus enabling G-XML to be written as a GML application schema. This resulted in many new types entering GML’s core object list, including observations, dynamic features, temporal objects, default styles, topology, and viewpoints. Much of the work was conducted by Galdos under contract to NTT Data. This laid the foundation for GML 3, although a significant new development occurred in this time frame, namely the intersection of the OGC and ISO/TC 211.

Towards ISO - GML 3.0 broadens the scope of GML

While a basic coding existed for most of the new objects introduced by the GML/G-XML agreement, and for some introduced by Galdos within the OGC process (notably coverages), it soon became apparent that few of these encodings were compliant with the abstract specifications developed by the ISO TC/211, specifications which were increasingly becoming the basis for all OGC specifications. GML geometry, for example, had been based on an earlier and only partly documented geometry model (Simple Features Geometry) and this was insufficient to support the more extensive and complex geometries described in TC/211. The management of GML development was also altered in this time frame with the participation of many more individuals. Significant contributions in this time frame were made by Milan Trninic (Galdos) (default styles, CRS), Ron Lake (Galdos) (Observations), Richard Martell (Galdos) (dynamic features).

On June 12, 2002, Mr. Ron Lake was recognized by the OGC for his work in creating GML by being presented the Gardels award.[14] The citation on the award reads “In particular, this award recognizes your great achievement in creating the Geography Markup Language, (GML), and your uniquely sensitive and effective work to promote the reconciliation of national differences to promote meaningful standardization of GML on a global level.” Simon Cox (CSIRO)[15] and Clemens Portele (Interactive Instruments)[16] also subsequently received the Gardels award, in part for their contributions to GML.

Standards

The Open Geospatial Consortium (OGC) is an international voluntary consensus standards organization whose members maintain the Geography Markup Language standard. The OGC coordinates with the ISO TC 211 standards organization to maintain consistency between OGC and ISO standards work. GML was adopted as an International Standard (ISO 19136:2007) in 2007.

GML can also be included in version 2.1 of the United States National Information Exchange Model (NIEM).

ISO 19136

ISO 19136 Geographic information – Geography Markup Language, is a standard from the family ISO - of the standards for geographic information (ISO 191xx). It resulted from unification of the Open Geospatial Consortium definitions and Geography Markup Language (GML) with the ISO-191xx standards.

Earlier versions of GML were not ISO conformal (GML 1, GML 2) with GML version 3.1.1. ISO conformity means in particular that GML is now also an implementation of ISO 19107.

The Geography Markup Language (GML) is an XML encoding in compliance with ISO 19118 for the transport and storage of geographic information modelled according to the conceptual modelling framework used in the ISO 19100-series and including both the spatial and nonspatial properties of geographic features. This specification defines the XML Schema syntax, mechanisms, and conventions that:

  • Provide an open, vendor-neutral framework for the definition of geospatial application schemas and objects;
  • Allow profiles that support proper subsets of GML framework descriptive capabilities;
  • Support the description of geospatial application schemas for specialized 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.

See also

References

  1. ^ Open Geospatial Consortium Inc. (2010-02-08), Technical Committee Policies and Procedures: MIME Media Types for GML (PDF)
  2. ^ "OpenGIS Geography Markup Language (GML) Encoding Standard". Retrieved 2011-03-25.
  3. ^ http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=56734
  4. ^ CityGML homepage
  5. ^ http://ndg.badc.rl.ac.uk/csml/
  6. ^ http://www.earthbyte.org/Resources/GPGIM/
  7. ^ http://inspire.ec.europa.eu/schemas/
  8. ^ "Archived copy". Archived from the original on 2010-03-23. Retrieved 2007-04-10.CS1 maint: Archived copy as title (link)
  9. ^ "Archived copy". Archived from the original on 2013-05-05. Retrieved 2011-10-12.CS1 maint: Archived copy as title (link)
  10. ^ http://www.ogcnetwork.net/node/220
  11. ^ https://developers.google.com/kml/documentation/kmlreference
  12. ^ "G-XML". Archived from the original on 2009-12-17.
  13. ^ "GML in JPEG 2000 for Geographic Imagery (GMLJP2) Encoding Specification".
  14. ^ award citation for Ron Lake
  15. ^ award citation for Simon Cox
  16. ^ award citation for Clemens Portele

External links

AIXM

The Aeronautical Information Exchange Model (AIXM) is designed to enable the management and distribution of Aeronautical Information Services (AIS) data in digital format. AIXM is based on Geography Markup Language (GML) and is one of the GML Application Schemas which is applicable for the Aeronautical domain. It was developed by the US Federal Aviation Administration (FAA), the US National Geospatial Intelligence Agency (NGIA) and the European Organisation for the Safety of Air Navigation (EUROCONTROL).The current version is AIXM 5.1.1.

CityGML

CityGML is an open standardised data model and exchange format to store digital 3D models of cities and landscapes. It defines ways to describe most of the common 3D features and objects found in cities (such as buildings, roads, rivers, bridges, vegetation and city furniture) and the relationships between them. It also defines different standard levels of detail (LoDs) for the 3D objects, which allows the representation of objects for different applications and purposes, such as simulations, urban data mining, facility management, and thematic inquiries.

CityGML is implemented as a GML application schema for the Geography Markup Language 3 (GML3), the extendible international standard for spatial data exchange issued by the Open Geospatial Consortium (OGC) and the ISO TC211.

Comparison of GIS vector file formats

The following tables compare general and technical information for a number of vector GIS file formats. Please see the individual products' articles for further information. Unless otherwise specified in footnotes, comparisons are based on the stable versions without any add-ons, extensions or external programs.

Coverage data

A coverage is the digital representation of some spatio-temporal phenomenon. ISO 19123 provides the definition:

[a] feature that acts as a function to return values from its range for any direct position within its spatial, temporal or spatiotemporal domainCoverages play an important role in geographic information systems (GIS), geospatial content and services, GIS data processing, and data sharing.

A coverage is represented by its "domain" (the universe of extent) and a collection representing the coverage's values at each defined location within its range. For example, a satellite image derived from remote sensing might record varying degrees of light pollution. Aerial photography, land cover data, and digital elevation models all provide coverage data. Generally, a coverage can be multi-dimensional, such as 1-D sensor timeseries, 2-D satellite images, 3-D x/y/t image time series or x/y/z geo tomograms, or 4-D x/y/z/t climate and ocean data.

However, coverages are more general than just regularly gridded imagery. The corresponding standards (see below) address regular and irregular grids, point clouds, and general meshes.

An interoperable service definition for navigating, accessing, processing, and aggregation of coverages is provided by the Open Geospatial Consortium (OGC) Web Coverage Service (WCS) suite and Web Coverage Processing Service (WCPS), a spatio-temporal coverage query language.

GPS Exchange Format

GPX, or GPS Exchange Format, is an XML schema designed as a common GPS data format for software applications. It can be used to describe waypoints, tracks, and routes. The format is open and can be used without the need to pay license fees. Location data (and optionally elevation, time, and other information) is stored in tags and can be interchanged between GPS devices and software. Common software applications for the data include viewing tracks projected onto various map sources, annotating maps, and geotagging photographs based on the time they were taken.

GeoRSS

GeoRSS is a specification for encoding location as part of a Web feed. (Web feeds are used to describe feeds ("channels") of content, such as news articles, Audio blogs, video blogs and text blog entries. These web feeds are rendered by programs such as aggregators and web browsers.) The name "GeoRSS" is derived from RSS, the most known Web feed and syndication format.

In GeoRSS, location content consists of geographical points, lines, and polygons of interest and related feature descriptions. GeoRSS feeds are designed to be consumed by geographic software such as map generators. By building these encodings on a common information model, the GeoRSS collaboration is promoting interoperability and "upwards-compatibility" across encodings.

At this point, the GeoRSS collaboration has completed work on two primary encodings that are called GeoRSS Geography Markup Language (GML) and GeoRSS Simple. GeoRSS-Simple is a very lightweight format that supports basic geometries (point, line, box, polygon) and covers the typical use cases when encoding locations. GeoRSS GML is a formal Open Geospatial Consortium (OGC) GML Application Profile, and supports a greater range of features than GeoRSS Simple, notably coordinate reference systems other than WGS84 latitude/longitude. There is also a W3C GeoRSS serialization, which is older and partly deprecated but still the most widely used.

GeoRSS can be used to extend both RSS 1.0 and 2.0, as well as Atom, the IETF's latest standard for feeds.

GeoSPARQL

GeoSPARQL is a standard for representation and querying of geospatial linked data for the Semantic Web from the Open Geospatial Consortium (OGC). The definition of a small ontology based on well-understood OGC standards is intended to provide a standardized exchange basis for geospatial RDF data which can support both qualitative and quantitative spatial reasoning and querying with the SPARQL database query language.The Ordnance Survey Linked Data Platform uses OWL mappings for GeoSPARQL equivalent properties in its vocabulary. The LinkedGeoData data set is a work of the Agile Knowledge Engineering and Semantic Web (AKSW) research group at the University of Leipzig, a group mostly known for DBpedia, that uses the GeoSPARQL vocabulary to represent OpenStreetMap data.

In particular, GeoSPARQL provides for:

a small topological ontology in RDFS/OWL for representation using

Geography Markup Language (GML) and well-known text representation of geometry (WKT) literals, and

Simple Features, RCC8, and DE-9IM (a.k.a. Clementini, Egenhofer) topological relationship vocabularies and ontologies for qualitative reasoning, and

a SPARQL query interface using

a set of topological SPARQL extension functions for quantitative reasoning, and

a set of Rule Interchange Format (RIF) Core inference rules for query transformation and interpretation.

Geospatial metadata

Geospatial metadata (also geographic metadata, or simply metadata when used in a geographic context) is a type of metadata that is applicable to objects that have an explicit or implicit geographic extent, i.e. are associated with some position on the surface of the globe. Such objects may be stored in a geographic information system (GIS) or may simply be documents, data-sets, images or other objects, services, or related items that exist in some other native environment but whose features may be appropriate to describe in a (geographic) metadata catalog (may also be known as a data directory or data inventory).

Integrated Transport Network

The Integrated Transport Network (ITN) is a dataset containing details of Great Britain's transport network. Produced by Ordnance Survey – the national mapping agency of Great Britain – it forms part of the OS MasterMap suite of products.

Intended to facilitate route planning and resource management, the dataset consists of three elements: Road Network (road geometry), Road Routing Information (routing information for drivers concerning mandatory and banned turns and other restrictions) and Urban Paths (man-made path geometry in urban areas).

The network is a link-and-node based network containing such details about each link as:

the class of road (A-road, B-road, etc.);

the nature of the road (single carriageway, dual carriageway, roundabout, etc.);

road names;

road routing information (RRI) (e.g. prohibited turns, one-way streets).These data are supplied in Geography Markup Language file format.

Keyhole Markup Language

Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers. KML was developed for use with Google Earth, which was originally named Keyhole Earth Viewer. It was created by Keyhole, Inc, which was acquired by Google in 2004. KML became an international standard of the Open Geospatial Consortium in 2008. Google Earth was the first program able to view and graphically edit KML files. Other projects such as Marble have also started to develop KML support.

List of document markup languages

The following is a list of document markup languages. You may also find the List of markup languages of interest.

OpenLayers

OpenLayers is an open-source (provided under the 2-clause BSD License) JavaScript library for displaying map data in web browsers as slippy maps. It provides an API for building rich web-based geographic applications similar to Google Maps and Bing Maps.

Open Geospatial Consortium

The Open Geospatial Consortium (OGC), an international voluntary consensus standards organization, originated in 1994. In the OGC, more than 500 commercial, governmental, nonprofit and research organizations worldwide collaborate in a consensus process encouraging development and implementation of open standards for geospatial content and services, sensor web and Internet of Things, GIS data processing and data sharing.

Simple Features

Simple Features (officially Simple Feature Access) is both an Open Geospatial Consortium (OGC) and International Organization for Standardization (ISO) standard ISO 19125 that specifies a common storage and access model of mostly two-dimensional geometries (point, line, polygon, multi-point, multi-line, etc.) used by geographic information systems.

The ISO 19125 standard comes in two parts. Part one, ISO 19125-1 (SFA-CA for "common architecture"), defines a model for two-dimensional simple features, with linear interpolation between vertices. The data model defined in SFA-CA is a hierarchy of classes. This part also defines representation using Well-Known Text (and Binary). Part 2 of the standard, ISO 19125-2 (SFA-SQL), defines an implementation using SQL. The OpenGIS standard(s) cover implementations in CORBA and OLE/COM as well, although these have lagged behind the SQL one and are not standardized by ISO.

The ISO/IEC 13249-3 SQL/MM Spatial extends the Simple Features data model mainly with circular interpolations (e.g. circular arcs) and adds other features like coordinate transformations and methods for validating geometries as well as Geography Markup Language support.

WXXM (data model)

The Weather Information Exchange Model (WXXM) is designed to enable the management and distribution of weather data in digital format (XML). WXXM version 2.0, set to be finalized in 2014, is based on Geography Markup Language (GML) and is one of the GML Application Schemas. It is being developed by the US Federal Aviation Administration (FAA) and the European Organisation for the Safety of Air Navigation (EUROCONTROL). WXXM is a member of a family of data models designed for use in aviation safety, notably Aeronautical Information Exchange Model (AIXM) and the Flight Information Exchange Model (FIXM).

WaterML

WaterML is a technical standard and information model used to represent hydrological time series structures. The current version is WaterML 2.0, released an open standard of the Open Geospatial Consortium (OGC).

Web Feature Service

In computing, the Open Geospatial Consortium Web Feature Service (WFS) Interface Standard provides an interface allowing requests for geographical features across the web using platform-independent calls. One can think of geographical features as the "source code" behind a map, whereas the WMS interface or online tiled mapping portals like Google Maps return only an image, which end-users cannot edit or spatially analyze. The XML-based GML furnishes the default payload-encoding for transporting geographic features, but other formats like shapefiles can also serve for transport. In early 2006 the OGC members approved the OpenGIS GML Simple Features Profile. This profile is designed both to increase interoperability between WFS servers and to improve the ease of implementation of the WFS standard.

The OGC membership defined and maintains the WFS specification. Numerous commercial and open-source implementations of the WFS interface standard exist, including the open-source reference implementations GeoServer and deegree. The OGC Implementing Products page

provides a comprehensive list of WFS implementations.

XLink

XML Linking Language, or XLink, is an XML markup language and W3C specification that provides methods for creating internal and external links within XML documents, and associating metadata with those links.

Standards of the Open Geospatial Consortium (OGC)
ISO standards by standard number
1–9999
10000–19999
20000+

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