# OS MasterMap Water Network Layer Technical Specification

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#### Product has reached its End of Life (withdrawal) date

The OS MasterMap Water Network Layer product (also referred to as OS MasterMap Networks – Water Layer) reached its End of Life on **31 March 2026**. As of this date, Ordnance Survey ceased to maintain or publish updates to the product, and access to the product was removed from the OS Data Hub, OS Features API and OS Vector Tile API. 

Supporting product documentation will be removed from this site 12 months after this date, when access to existing data packages in the OS Data Hub is no longer available. Full details, including migration information and FAQs, are available on the [OS MasterMap Water Network Layer End of Life information page](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/end-of-life-notice-os-mastermap-water-network-layer).
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OS MasterMap Water Network Layer provides a three-dimensional structured link and node network of Great Britain's watercourses. A link represents the approximate central alignment of a watercourse and includes inland rivers, streams, tidal water, lakes, lochs and canals; links are attributed with additional information, including flow direction and primary flow paths. Where watercourses are obscured or underground, connectivity is provided where Ordnance Survey capture processes or accepted sources can infer the connection.

The OS MasterMap Water Network Layer product is in geometric sympathy with the underlying topographic features that comprise OS MasterMap Topography Layer. Polygons and lines representing the water area and its banks are not supplied in this product but will continue to be maintained and supplied as part of the OS MasterMap Topography Layer product.

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FnyU7SFfrFAD2AXFlosGZ%2F1.png?alt=media" alt="Example extract from OS MasterMap Water Network Layer showing one large river and several tributaries/smaller rivers running into it. The WatercourseLink (blue solid lines) features and HydroNode features (small white circle with a blue solid outline) are shown on top of every watercourse."><figcaption><p><em>Example extract from OS MasterMap Water Network Layer showing WatercourseLink and HydroNode features.</em></p></figcaption></figure>

## Identifiers <a href="#id-1.1-identifiers" id="id-1.1-identifiers"></a>

Ordnance Survey provides persistent managed identifiers as TOIDs. TOIDs are strings of up to twenty characters, starting with ‘osgb’; the remaining characters are digits (0 to 9). In an INSPIRE encoded dataset such as this, each feature carries its identifier in three ways, as described below:

* **gml:id:** Required by Geography Markup Language (GML). This matches the pattern in other OS MasterMap products.
* **gml:identifier:** Recommended by INSPIRE and the UK INSPIRE project. This formats the TOID into a persistent URI, using [`http://data.os.uk/id/`](http://data.os.uk/id/) as a namespace, instead of `‘osgb’`. This does not mean that the water network features are available as linked data.
* **net:inspireId:** The `localId` is set to the TOID (without `‘osgb’`), and the namespace set as above. The INSPIRE identifier model does not fit with SF0; it does fit with level 1.

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2F0H4Z4E2lIMSgCq2UIxxh%2F2.png?alt=media" alt="An example of a feature in an INSPIRE encoded dataset carrying its identifier in three ways."><figcaption><p><em>An example of a feature in an INSPIRE encoded dataset carrying its identifier in three ways.</em></p></figcaption></figure>

The feature version is encoded as the `versionId` within the INSPIRE identifier.

## Available formats for the product <a href="#id-1.2-available-formats-for-the-product" id="id-1.2-available-formats-for-the-product"></a>

OS MasterMap Water Network Layer will be supplied in Geography Markup Language (GML) 3.2.1, GeoPackage and vector tiles formats.

## Adherence to standards <a href="#id-1.3-adherence-to-standards" id="id-1.3-adherence-to-standards"></a>

OS MasterMap Water Network Layer is based on the INSPIRE Hydrography Data Specification, which itself is based on the ISO TC211 family of open standards.

## Extending INSPIRE specification <a href="#id-1.3.1-extending-inspire-specification" id="id-1.3.1-extending-inspire-specification"></a>

OS MasterMap Water Network Layer extends the INSPIRE specification.

## UML diagram and table conventions <a href="#id-1.3.2-uml-diagram-and-table-conventions" id="id-1.3.2-uml-diagram-and-table-conventions"></a>

The data structure is described below by means of unified modelling language (UML) class diagrams and accompanying tables containing text. The UML diagrams conform to the approach specified in ISO 19103 Conceptual schema language and ISO 19109 Rules for application schema, as adopted by INSPIRE.

Colour conventions have been used in the diagrams and tables to distinguish the INSPIRE specification from the additional properties that have been added in this specification. In the UML diagram, classes from the INSPIRE Data Specifications are coloured grey, whereas classes in the Ordnance Survey product specification are coloured orange. All code lists are coloured blue, enumerations are coloured green and data types are coloured purple, which can be seen in the UML diagram below.

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FPNA9Ih4Q5NVosh1ck99h%2F3.jpeg?alt=media" alt="An example UML diagram using the colour conventions specified in this Technical Specification. Grey indicates an INSPIRE Feature Type; orange indicates an OS MasterMap Water Network Layer feature type; blue indicates a code list and green indicates an enumeration."><figcaption><p><em>A UML diagram using the colour conventions specified in this Technical Specification.</em></p></figcaption></figure>

## Index

This technical specification includes the following sections:

* [Product notes](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/product-notes)
* [Product structure](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/product-structure)
* [Feature types](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/feature-types)
* [Structured data types](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/structured-data-types)
* [Code lists and enumerations](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/code-lists-and-enumerations)
* [Feature types for future release](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/feature-types-for-future-release)
* [GML overview](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/gml-overview)
* [GeoPackage overview](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/geopackage-overview)
* [Vector tiles overview](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/vector-tiles-overview)
* [Data provenance](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/data-provenance)
* [Additional resources](https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/additional-resources)


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