> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/transport-network-portfolio/os-mastermap-highways-network-roads/os-mastermap-highways-network-roads-technical-specification/gml-overview.md).

# GML overview

This section describes how OS MasterMap Highways Network is defined in GML. An understanding of XML (Extensible Mark-up Language) and XML schema is required.

GML is an XML grammar for expressing geographic features. GML serves as a modelling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. More information can be found on the Open Geospatial Consortium (OGC). <http://www.opengeospatial.org/standards/gml>.

The XML specifications that GML is based on are available from the World Wide Web Consortium (W3C): [http://www.w3.org](http://www.w3.org/).

Information about Unicode and UTF-8, the character encoding we have chosen, is available on the Unicode Consortium website: [http://www.unicode.org](http://www.unicode.org/).

## Schema overview and location <a href="#bookmark94" id="bookmark94"></a>

XML schemas are used to define and validate the format and content of GML. The GML 3.2 specification provides a set of schemas that define the GML feature constructs and geometric types. These are designed to be used as a basis for building application-specific schemas, which define the data content.

The Road Network uses the following application schemas; LinearHighwayNetwork.xsd, HighwaysWaterTransportNetwork.xsd and OSProducts.xsd which are referenced by the data. The LinearHighwaysNetwork.xsd defines the features which make up the Road Network. Therefore, it imports the INSPIRE transport network road application schema. The HighwaysWaterTransportNetwork.xsd defines the features which make up the Ferry Network. Therefore, it imports the INSPIRE transport network water application schema. Through the INSPIRE schemas both the LinearHighwayNetwork.xsd and HighwaysWaterTransportNetwork.xsd import the GML 3.2 schemas. These in turn import schemas produced by the W3C, which are available from the W3C website at [http://www.w3.org/XML/1998/namespace.html.](http://www.w3.org/XML/1998/namespace.html) The OSProducts.xsd defines the feature collection and feature members. In addition, this application schema will define the transactions used for a Change Only Update supply.

The Linear Highway Network schema document defines the `http://namespaces.os.uk/mastermap/highwayNetwork/2.0` namespace,

this is defined in the XSD at: <https://www.ordnancesurvey.co.uk/xml/schema/highwaysnetwork/2.0/LinearHighwayNetwork.xsd>

The Highways Water Transport Network schema document defines the `http://namespaces.os.uk/mastermap/highwaysWaterTransportNetwork/1.0` namespace,

this is defined in the XSD at: <http://www.os.uk/xml/schema/highwaysnetwork/1.0/linearhighwaynetwork.xsd>.

The application schema uses the following XML namespaces and their associated definitions:

<table data-full-width="true"><thead><tr><th width="145">Prefix</th><th width="462">Namespace identifier</th><th>Definition available at</th></tr></thead><tbody><tr><td>gml</td><td><code>http://www.opengis.net/gml</code></td><td><a href="http://schemas.opengis.net/gml/3.2.1/gml.xsd">http://schemas.opengis.net/gml/3.2.1/gml.xsd</a></td></tr><tr><td>xsi</td><td><code>http://www.w3.org/2001/XMLSchema–instance</code></td><td>Built in to XML <a href="http://www.w3.org/TR/xmlschema-1/">http://www.w3.org/TR/xmlschema-1/</a></td></tr><tr><td>xlink</td><td><code>http://www.w3.org/1999/xlink</code></td><td><a href="http://www.w3.org/1999/xlink.xsd">http://www.w3.org/1999/xlink.xsd</a></td></tr><tr><td>net</td><td><code>http://inspire.ec.europa.eu/schemas/net/4.0</code></td><td><a href="http://inspire.ec.europa.eu/schemas/net/4.0/Network.xsd">http://inspire.ec.europa.eu/schemas/net/4.0/Net</a> <a href="http://inspire.ec.europa.eu/schemas/net/4.0/Network.xsd">work.xsd</a></td></tr><tr><td>tn</td><td><code>http://inspire.ec.europa.eu/schemas/tn/4.0</code></td><td><a href="http://inspire.ec.europa.eu/schemas/tn/4.0/CommonTransportElements.xsd">http://inspire.ec.europa.eu/schemas/tn/4.0/Com</a> <a href="http://inspire.ec.europa.eu/schemas/tn/4.0/CommonTransportElements.xsd">monTransportElements.xsd</a></td></tr><tr><td>tn-ro</td><td><code>http://inspire.ec.europa.eu/schemas/tn-ro/4.0</code></td><td><a href="http://inspire.ec.europa.eu/schemas/tn-ro/4.0/RoadTransportNetwork.xsd">http://inspire.ec.europa.eu/schemas/tn-</a> <a href="http://inspire.ec.europa.eu/schemas/tn-ro/4.0/RoadTransportNetwork.xsd">ro/4.0/RoadTransportNetwork.xsd</a></td></tr><tr><td>tn-w</td><td><code>http://inspire.ec.europa.eu/schemas/tn-w/4.0</code></td><td><a href="http://inspire.ec.europa.eu/schemas/tn-w/4.0/WaterTransportNetwork.xsd">http://inspire.ec.europa.eu/schemas/tn-</a> <a href="http://inspire.ec.europa.eu/schemas/tn-w/4.0/WaterTransportNetwork.xsd">w/4.0/WaterTransportNetwork.xsd</a></td></tr><tr><td>os</td><td><code>http://namespaces.os.uk/product/1.0</code></td><td><a href="http://www.ordnancesurvey.co.uk/xml/schema/product/1.0/OSProduct.xsd">http://www.ordnancesurvey.co.uk/xml/schema/</a> <a href="http://www.ordnancesurvey.co.uk/xml/schema/product/1.0/OSProduct.xsd">product/1.0/OSProduct.xsd</a></td></tr><tr><td>network</td><td><code>http://namespaces.os.uk/mastermap/generalNetwork/2.0</code></td><td><p><a href="https://www.ordnancesurvey.co.uk/xml/schema/network/2.0/generalNetwork.xsd">https://www.ordnancesurvey.co.uk/xml/schema</a></p><p><a href="https://www.ordnancesurvey.co.uk/xml/schema/network/2.0/generalNetwork.xsd">/network/2.0/generalNetwork.xsd</a></p></td></tr><tr><td>highway</td><td><code>http://namespaces.os.uk/mastermap/highwayNetwork/2.0</code></td><td><a href="http://www.os.uk/xml/schema/highwaysnetwork/2.0/LinearHighwayNetwork.xsd">http://www.os.uk/xml/schema/highwaysnetwor</a> <a href="http://www.os.uk/xml/schema/highwaysnetwork/2.0/LinearHighwayNetwork.xsd">k/2.0/LinearHighwayNetwork.xsd</a></td></tr><tr><td>ram</td><td><code>http://namespaces.os.uk/mastermap/routingAndAssetManagement/2.1</code></td><td><a href="http://www.os.uk/xml/schema/highwaysnetwork/2.1/RoutingAndAssetManagement.xsd">http://www.os.uk/xml/schema/highwaysnetwor</a> <a href="http://www.os.uk/xml/schema/highwaysnetwork/2.1/RoutingAndAssetManagement.xsd">k/2.1/RoutingAndAssetManagement.xsd</a></td></tr><tr><td>hwtn</td><td><code>http://namespaces.os.uk/mastermap/highwaysWaterTransportNetwork/1.0</code></td><td><a href="http://www.os.uk/xml/schema/highwaysnetwork/v1/HighwaysWaterTransportNetwork.xsd">http://www.os.uk/xml/schema/highwaysnetwor</a> <a href="http://www.os.uk/xml/schema/highwaysnetwork/v1/HighwaysWaterTransportNetwork.xsd">k/v1/HighwaysWaterTransportNetwork.xsd</a></td></tr><tr><td>dedication</td><td><code>http://namespaces.os.uk/mastermap/highwayDedication/1.0</code></td><td><p><a href="https://www.ordnancesurvey.co.uk/xml/schema/highwaysnetwork/1.0/HighwayDedication.xsd">https://www.ordnancesurvey.co.uk/xml/schema</a></p><p><a href="https://www.ordnancesurvey.co.uk/xml/schema/highwaysnetwork/1.0/HighwayDedication.xsd">/highwaysnetwork/1.0/HighwayDedication.xsd</a></p></td></tr></tbody></table>


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