OS MasterMap Networks - Water Layer | Data Products | OSOrdnance Survey

OS MasterMap Water Network Layer is a three-dimensional digital representation of Great Britain's watercourses. The product includes rivers, streams, lakes, lochs and canals as a series of watercourse network lines. The network lines (links) are attributed to provide a range of information about the section of watercourse they depict. OS MasterMap Water Network Layer will significantly enhance systems used to manage waterways and rivers and the flood risk they pose.

How to get this product

Access to this product is free for Public Sector Geospatial Agreement (PSGA) Members. Find out if you are a PSGA Member or download a sample of OS MasterMap Water Network Layer data by accessing the product page on the OS website, which has links to all of the relevant resources. Alternatively, you can try out the full product by applying for a Data Exploration license.

Visualise OS MasterMap Water Network Layer data online

This product is available to try out online using one of our three sets of sample data (Exeter, Newport and Inverness) through the OS MasterMap Product Viewer:

OS MasterMap Product Viewer

Interactive demonstrator of OS MasterMap Generation data

# Other ways to access this data

MasterMap Water Network Layer data is available from our OS Features API, providing location-based insights combining topography data with buildings, transport, and water layer data to create finely detailed datasets with a high degree of accuracy. Find out more about our OS API platform here to unlock access to rich geospatial data and integrate OS data and services into your applications.

Access to MasterMap Water Network Layer data is also available through the OS NGD Water Theme, providing a three-dimensional structured link and note network of watercourses for Great Britain. Users may find that NGD Water Theme data is more accessible, contains greater attribution, and is easier to use with databases and GIS software. Find out more about NGD data here to discover how to access OS NGD and what's available to users.

What's next?

To access additional documentation and resources relating to this product, please refer to the following:

Overview

The overview introduces OS MasterMap Water Network Layer and gives context for all users – highlighting key features, providing examples of uses, and listing details such as file sizes, etc.

Getting Started Guide

The getting started guide provides instructions for using OS MasterMap Water Network Layer in different applications. Users with limited technical knowledge will be able to follow this guide.

Technical Specification

The technical specification provides detailed technical information about OS MasterMap Water Network Layer. It is targeted at technical users and software developers.

OS MasterMap Water Network Layer – January 2025 release note

This release note provides information about the January 2025 release of OS MasterMap Water Network Layer.

OS MasterMap Water Network Layer – October 2024 release note

This release note provides information about the October 2024 release of OS MasterMap Water Network Layer.

OS MasterMap Water Network Layer – April 2024 release note

This release note provides information about the April 2024 release of OS MasterMap Water Network Layer.

OS MasterMap Water Network Layer – January 2024 release note

This release note provides information about the January 2024 release of OS MasterMap Water Network Layer.

Feature counts

Errors

Product improvements

Tiles containing no data are no longer published.

Next release

The next release of OS MasterMap Water Network Layer is scheduled for April 2025.

Feature counts

Errors

Product improvements

Tiles containing no data are no longer published.

Next release

The next release of OS MasterMap Water Network Layer is scheduled for January 2025.

Feature counts

Errors

Product improvements

Tiles containing no data are no longer published.

Next release

The next release of OS MasterMap Water Network Layer is scheduled for July 2024.

Feature counts

Errors

Product improvements

Tiles containing no data are no longer published.

Next release

The next release of OS MasterMap Water Network Layer is scheduled for April 2024.

OS MasterMap Water Network Layer is a three-dimensional digital representation of Great Britain's watercourses. The product includes rivers, streams, lakes, lochs and canals as a series of watercourse network lines. The network lines (links) are attributed to provide a range of information about the section of watercourse they depict. OS MasterMap Water Network Layer will significantly enhance systems used to manage waterways and rivers and the flood risk they pose.

Watercourses that are underground or below structures are included where Ordnance Survey capture processes or accepted sources can infer the connection.

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.

OS MasterMap Water Network Layer is provided with three-dimensional coordinates.

Key features of the product

The OS MasterMap Water Network Layer product includes the following key features:

• Flow and connectivity.

• Three-dimensional geometry.

• Catchment information including name.

• The names of watercourses, including language alternatives.

• Vertical relationships where water courses pass over or under one other.

• Average widths.

• Additional information provided by national authorities.

Product applications

OS MasterMap Water Network Layer supports a wide range of customer applications that use geographic information. The product can be used alone or in combination with other Ordnance Survey products, such as OS MasterMap Topography Layer, OS MasterMap Imagery Layer and OS Terrain 5.

The OS MasterMap Water Network Layer product could be used for applications such as:

• Understanding flood risk

• Flood risk mitigation planning

• Flood response planning and execution

• Detailed flood modelling for insurance and land and property

• Environmental impact analysis

• Tracking water flows and any contamination

• Asset management and protection

• The management of statutory directives relating to watercourses

• Ecology studies, for example, species migration

• Analytics and visual interpretation, particularly when used in combination with other Ordnance Survey products, for example, OS Terrain 5

Index

This overview includes the following sections:

• Feature types in the product

• Standards and CRS

• Product supply

OS MasterMap Water Network Layer features are classified into feature types. Each feature type has associated attribution, and further detail can be found in the OS MasterMap Water Network Layer Technical Specification.

The product has two core feature types: WatercourseLink and HydroNode.

WatercourseLink Feature Type

A WatercourseLink feature represents the alignment of a watercourse; the majority have been derived from Ordnance Survey's detailed topographic data, made available to customers as the

OS MasterMap Topography Layer product.

WatercourseLink features are split in the following circumstances:

• Where two or more watercourses meet

• Where the real-world-based attribution of a watercourse changes

• Where the name of a watercourse changes or ceases to apply

WatercourseLink features are not split where they pass under or over one another at different levels. They may be split where they pass into a culvert or tunnel or onto an aqueduct.

Height has been added to each vertex coordinate using the raw data used to create the OS Terrain height products.

HydroNode Feature Type

A HydroNode feature explicitly represents the source, sink or junction of a watercourse. In addition, they record the location where any real-world-related attribution changes.

A HydroNode feature may only exist at the end point of a WatercourseLink feature. Height has been added to the coordinate for the HydroNode using the raw data used to create the OS Terrain height products.

Standards

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

Coordinate reference system (CRS)

OS MasterMap Water Network Layer uses the British National Grid (BNG) spatial reference system. BNG uses the OSGB36 geodetic datum and a single Transverse Mercator projection for the whole of Great Britain. Positions on this projection are described using easting and northing coordinates in units of metres. The BNG is a horizontal spatial reference system only; it does not specify a vertical (height) reference system.

This water network product, unlike other OS MasterMap layers, contains height values for the geometry vertices. Several orthometric height datums are used in OS MasterMap data to define vertical spatial reference systems; the most common of these is Ordnance Datum Newlyn (ODN), which is used throughout mainland Britain. Height values on the features do not specify which vertical reference system is used, although information on the extents of additional datums can be provided.

OS MasterMap Water Network Layer is projected in the ESPG 7405 OSGB36 / British National Grid + ODN. This projection is used as it specifies the Z value as ODN.

In the Geography Markup Language (GML) data, this is represented by reference to its entry in the EPSG registry.

The GeoPackage product format is in the BNG projection (BNG: 27700).

The vector tiles product format is in the Web Mercator projection (EPSG:3857). This projection is a global coordinate reference system.

Please see A Guide to Coordinate Systems in Great Britain on our More than Maps platform for more information on CRSs.

Available formats for the product

OS MasterMap Water Network Layer is available in three formats:

• Geography Markup Language (GML) 3.2.1, zipped using gzip

• GeoPackage file, zipped using gzip

• Vector tiles (MBTiles) file, zipped using gzip

Product supply mechanism

OS MasterMap Water Network Layer incorporates a web-based ordering system that allows customers to order their initial data supply and any updates, obtain price estimates and view details of their holdings on demand. The product is supplied as an online download. You can download data in various formats from the OS Data Hub.

Coverage and file size

For GML, OS MasterMap Water Network Layer is a national dataset and is maintained and supplied as 5km by 5km tiles of data. File size estimates can vary from about 1 Kb compressed to about 780 Kb (compressed). A full national supply will be approximately 1.25Gb compressed. Compression rates vary and are dependent on the size and content of a tile.

For GeoPackage and vector tiles, the coverage will be Great Britain (GB) only. The file size is 1.8Gb zipped for GeoPackage and 1.5Gb zipped for vector tiles.

Geographic chunking

To make the management of large areas easier, data is split into chunks, each of which covers a nominal square area or part of such a square or a nominated size. Chunk boundaries are imposed purely for the purpose of dividing large supply areas into pieces of a manageable size in a geographically meaningful way. Both full supply and updates are chunked.

The following steps describe how data is chunked into geographic areas:

1. The customer submits an area of interest (AOI).

2. The online system creates a grid covering the entire area based on specified size; any 5km by 5km chunk that intersects the AOI will be included in the order.

3. Each square grid forms a chunk file.

4. Each feature that intersects that square goes into the chunk file.

5. OS MasterMap Water Network Layer is supplied in 5km by 5km chunks.

Where WatercourseLink features go over tile edges they are supplied in every chunk they intersect. Therefore, these features will be duplicated. Systems reading OS MasterMap data must identify and provide the option to remove these duplicate features.

Empty chunks are not supplied; that is, if a chunk contains no information relating to a customer’s selected themes, then it would be an empty file and it would not be supplied.

Change-only update (COU)

OS MasterMap Water Network Layer changes are supplied on a chunk basis. When a feature is changed, all chunks that contain that feature are flagged as containing an update. Within an updated chunk, all features are supplied whether changed or not. Inspection of the individual metadata attributes can highlight whether any individual feature has been updated.

Currency

OS MasterMap Water Network Layer is supplied to customers quarterly in January, April, July and October, incorporating any updates made by the revision programme.

OS MasterMap Water Network Layer is a digital representation of the watercourses in Great Britain as a series of connected features. The data represents the approximate central alignment of watercourses and is attributed to provide a range of information about the section of watercourses they represent.

The product has two core feature types:

• WatercourseLink: A WatercourseLink feature represents the alignment of a watercourse. The majority have been derived from Ordnance Survey detailed topographic data, made available to customers as the OS MasterMap Topography Layer product.

• HydroNode: A HydroNode feature explicitly represents the start, junctions and end of each watercourse, as well as places where there's a change in the real-world-related attribution.

Index

This guide includes the following sections:

• Requirements for using the data

• Structure of the supplied data

• Loading GML data into a GIS

• Creating a water network using ESRI software

System requirements

OS MasterMap Water Network Layer is designed for use in a geographic information system (GIS). For details of Ordnance Survey’s Licensed Partners who can assist you with incorporating the product in their systems, please see the 'GIS software' page on the Ordnance Survey website.

Ordnance Survey does not recommend specific suppliers or software products, as the most appropriate system will depend on many factors, for example, the amount of data being taken, resources available within the organisation, the existing and planned information technology infrastructure, and, ultimately, the applications that the data will be used for. However, as a minimum, the following elements will be required in any system:

• A means of reading the data, either in its native format, or by translating it into a file format or for storage in a database.

• A means of storing and distributing the data, perhaps in a database or through a web-based service.

• A way of visualising and / or querying the data, typically a GIS.

Backup provision of the product

You are advised to copy the supplied data to a backup medium before following the steps outlined in this getting started guide.

Typical data volumes

For reading purposes, it is recommended that users store the data on a single hard disc. This will speed up the ability of your computer to read the data. Compressed file sizes for the full supply of England, Scotland and Wales are as follows:

• Geography Markup Language (GML): The compressed file size for Great Britain is approximately 1.25Gb.

• GeoPackage: The compressed file size for Great Britain is approximately 1.8Gb.

• Vector tiles: The compressed file size for Great Britain is approximately 1.5Gb.

OS MasterMap Water Network Layer is supplied in three formats: Geography Markup Language (GML 3.2.1), GeoPackage and vector tiles. All formats are compressed into a regular zip file (.ZIP).

Before loading the data, you will need to unzip it by using any of the regular zip programs available or via the facility within the Windows 10 operating system.

Area of interest order type

The tiled dataset will be provided in 5km x 5km square tiles and will contain all features present in the tile(s) ordered.

The data is supplied as 'hairy tiles', in that no feature is broken at the tile edge but is included across the tile boundary if it extends into an adjacent tile. As such, a data holding comprising more than one 5km² tile will contain duplicate features which may need to be removed depending upon the user requirement.

The GeoPackage and vector tiles formats will be available for Great Britain coverage only. The file naming convention will be as follows:

• GML: 5km² tile ID. gz, for example: HP4500.gz

• GeoPackage: MMNWGB.gpkg

• Vector tiles: MMNWGB.mbtiles

Data ordering and download

• Direct customers and Partners, please contact your Account Manager or Business Enquiries.

• For Public Sector Geospatial Agreement (PSGA) customers, the product is available to you through the PSGA Contract.

The data is available as an online download via the OS Data Hub.

Download contents

The data is supplied in a .zip archive, which contains a parent folder with two sub-folders entitled DATA and DOC, and an additional readme file.

Geography Markup Language (GML) is an XML dialect, which can be used to model geographic features. It was designed by the Open Geospatial Consortium (OGC) as a means for people to share information regardless of the particular applications or technology that they use. In the first instance, GML was used to overcome the differences between different geographic information system (GIS) applications by providing a neutral file format as an alternative to proprietary formats.

The data can be loaded into several GIS. This page describes how to translate the GML and load it into some commonly used GIS. For more information about other GIS that OS MasterMap Water Network Layer is compatible with, please speak to your Relationship Manager.

The common software covered in this section are as follows:

• QGIS

• FME

• ERSI ArcMap

• MapInfo Professional

• Cadcorp Map Modeller

OS MasterMap Water Network Layer data can be used in two types of networks.

Geometric network

Geometric networks offer a way to model common networks and infrastructures found in the real world. Water distribution and water flow in a stream are two examples of resource flows that can be modelled and analysed using a geometric network.

A geometric network can be set up easily, does not need an additional license and has some functionality (tracing up / downstream, for example) provided by the Utility Network Analyst Toolbar.

Network analyst

Network analyst is the mathematical processing of the geometry of a link / node layer, enabling the identification of all possible routes around that network, along with the distances and times involved. Put simply, this means that, using an accurate road data layer, the computer can identify possible routes between two locations and calculate the shortest route.

This requires a Network Analyst License. You can build simple networks, but more complicated networks will require you to have detailed knowledge of networks to set up attributes and elevators.

Building a geometric network

A geometric network is built within a feature dataset in the geodatabase. The feature classes in the feature dataset are used as the data sources for network junctions and edges. The following step-by-step instructions will guide you through building a geometric network; they have been prepared using ArcMap version 10.6.1.

1. Open ArcCatalog.

2. Navigate to your geodatabase in your Folder Connections.

3. Expand the geodatabase.

4. Right-click on the geodatabase, select New from the list of options, then click Feature Dataset…

1. Give your new Feature Dataset a name, then click Next.

1. Set your coordinate system that will be used for the XY coordinates in the data (British National Grid EPSG:27700), then click Next.

1. Set your coordinate system that will be used for the Z coordinates in the data (Newlyn). Ordnance Datum Newlyn (ODN) is our national coordinate system for heights above mean sea level (orthometric heights).

2. Click Next.

1. In the next panel, leave your XY tolerance as the default settings and click Finish. A new Feature Dataset will appear in the geodatabase.

1. Copy the HydroNode and WatercourseLink feature classes into the new Feature Dataset by simply dragging them in.

2. You may get an error message if the coordinate systems of the feature classes don’t match those of the new Feature Dataset. To resolve this, right-click on each feature class and select Properties. Check that the Z coordinate system is set to Newlyn and the XY coordinate system is set to British National Grid, then copy the feature classes into the new Feature Dataset.

1. Right-click the Water feature dataset in the geodatabase, select New from the list of options, then click Geometric Network.

1. Click Next in the New Geometric Network dialog box that opens.

1. Type the name of your geometric network into the text box under the Enter a name for your geometric network section.

2. Select Yes for the snap features within the specified tolerance option.

3. Type 0.5 in the text box next to Meters.

4. Click Next.

1. In the next panel, you must select which feature classes in the feature dataset will participate in the geometric network. Click Select All. All the feature classes in the list will participate in the network.

2. Click Next.

1. The option to exclude features with certain attributes makes it easier to manage the network. In the next panel, you need to opt not to exclude features. Click No, so that all features will participate in the geometric network.

2. Click Next.

1. In the next dialog box, you must specify which line classes will become complex edge feature classes in the geometric network. Complex edge features are not split into two features by the connection of another feature along their length; thus, they are useful for modeling water mains, which may have multiple laterals connected to them. By default, all line feature classes are simple edge feature classes. In the same dialog box, you must specify which, if any, of the junction feature classes can act as sources and sinks in the network. Sources and sinks are used to determine the flow direction in the network.

2. In the row for the HydroNode feature class, click Simple Junction under the Role column.

3. In the row for the WatercourseLink feature class, choose Complex Edge from the list under the Role column.

4. In the row for the HydroNode feature class, click the dropdown menu under the Sources & Sinks column, then click Yes.

5. Click Next.

1. This geometric network does not require weights, which is the default, so click Next in the following panel:

1. Clicking Next opens a summary page. Click Finish after you review the summary page.

2. A progress indicator will appear displaying the progress for each stage of the network-building process. You will receive an error message indicating that the network has been built but contains some errors:

1. Click OK to close the error message box.

2. You can see what errors occurred while building the geometric network by previewing the WaterNet_BUILDERR table.

3. Right-click the WaterNet_BUILDERR table in the Catalog and click Item Description. Then click the Preview tab to view the entries in this table.

4. Features with invalid geometries are identified during the network build progress and recorded in the Network Build Errors Table. (This is user-managed; it does not get updated when the features listed within it are edited.)

5. If you received more than two errors, delete the geometric network and repeat the steps to create it again.

6. You can then proceed to load the data into ArcMap.

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.

Identifiers

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/ 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.

The feature version is encoded as the versionId within the INSPIRE Identifier.

Available formats for the product

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

Adherence to standards

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

OS MasterMap Water Network Layer extends the INSPIRE specification.

UML diagram and table conventions

The data structure is described below by means of unified modeling 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 figure below. The tables which follow in this Technical Specification use orange for a feature type, blue for a code list, green for enumerations and purple for data types.

Index

This technical specification includes the following sections:

• Product notes

• Product structure

• Feature types

• Structured data types

• Code lists and enumerations

• Feature types for future release

• GML overview

• GeoPackage overview

• Vector tiles overview

• Data provenance

• Additional resources

The following documents outline observations made from product testing and observations which are of note to users of the product:

Product Notes January 2022

The following page outlines observations made from product testing and observations which are of note to users of the product. Ordnance Survey is working towards fixing these errors for the next release.

Language qualifiers

The xml:lang attributes are not populated in the product. They are planned for population in a future product release where a feature has more than one name.

Name continuity

The names of watercourses in the product are not all continuous throughout their extent.

HydroNode categories

There are a number of errors with HydroNode features with the hydroNodeCategory value 'Source' and 'Outlet', where the flowDirection of the connected WatercourseLink is in the wrong direction or is unknown.

Geometry issues

There are a number of WatercourseLink features which self-intersect. The vast majority are at the mm level and were created by rounding processes. These will be fixed in a future release.

There are a small number of WatercourseLink features which are shorter in length than 1m. There are a small number of WatercourseLink features which form a closed loop.

There are a number of double digitised WatercourseLink features across the product.

OS MasterMap Water Network Layer is a topological network representing the watercourses within Great Britain.

The product is made up of five feature types:

• WatercourseLink: Features that represent the approximate central alignment of a watercourse, including rivers, lakes and canals. They can represent part of a watercourse or a whole watercourse.

• HydroNode: Features that represent a river’s source, end, a junction where three or more links meet, and places where the real-world related attribution changes, for example, the point where a watercourse becomes tidal.

• WatercourseSeparatedCrossing: Features to indicate the relationships between watercourses that intersect at different levels.

• WatercourseLinkSet: Features to represent sets of links, for example, named rivers or watercourses within a catchment area.

• WatercourseInteraction: Features that represent events along the water network, for example, weirs and mooring points.

Only two feature types are supplied in the current release of the product: WatercourseLink and HydroNode. This technical specification will cover all five of the feature types which make up the product as all five feature types are referenced in the product schema, which is the controlling specification for the product.

All the feature instances, of whichever feature type, are provided as a single FeatureCollection.

OS MasterMap Water Network Layer has been built with the INSPIRE Hydro – Network Specification as a basis, which results in the product inheriting attribution from INSPIRE. An overview of the product structure can be found in the image below, which highlights the inherited INSPIRE feature types and attribution.

Properties of the INSPIRE specification which are voidable and are not being populated in the product have not been included in the class diagrams below or in the following feature type pages. For information on the INSPIRE properties which are not included in this product, please see the INSPIRE Data Specification on Hydrography – Network application schema.

This section describes the feature types which make up OS MasterMap Water Network Layer. The attributes associated with the feature types are listed on the following two pages. The following information is given for each attribute.

Feature type attribute information

Name and Definition

The name of the attribute and what it is describing.

Data type

The nature of the attribute, for example, a numeric value or a code list value.

Multiplicity

Describes how many times this element is expected to be populated in the data. An attribute may be optional or mandatory within the product. These are denoted by:

• ‘1’ – there must be a value.

• ‘0..1’ – population is optional but a maximum of one attribute will be returned. These values may be used in combination.

WatercourseLink features represent the alignments of watercourses and have, in the most part, been derived from Ordnance Survey detailed topographic data.

Where the classification or name changes along a watercourse, the network will be split and a HydroNode classified as 'Pseudo' will be created.

WatercourseLink attributes

A segment that represents part of a watercourse.

• Subtype of: WatercourseLink

centrelineGeometry

The three-dimensional geometry that represents the general alignment of the watercourse.

• Attribute name: centrelineGeometry

• Type: GM_Curve

• Multiplicity: [1]

ficticious

Indicator that the centreline geometry of the link is a straight line with no intermediate control points – unless the straight line represents the geography in the resolution of the data set appropriately.

• Attribute name: ficticious

• Type: Boolean

• Multiplicity: [1]

startNode

The HydroNode coincident with the first vertex for this WatercourseLink.

• Attribute name: startNode

• Multiplicity: [1]

endNode

The HydroNode coincident with the last vertex for this WatercourseLink. On very rare occasions, the end HydroNode may be the same instance as the start HydroNode.

• Attribute name: endNode

• Multiplicity: [1]

inspireId

External object identifier of the spatial object.

• Attribute name: inspireId

• Type: Identifier

• Multiplicity: [0..1]

versionId «lifeCycleInfo» «voidable»

The identifier of the particular version of the spatial object, with a maximum length of 25 characters. If the specification of a spatial object type with an external object identifier includes life-cycle information, the version identifier is used to distinguish between the different versions of a spatial object. Within the set of all versions of a spatial object, the version identifier is unique.

• Attribute name: versionId

• Type: CharacterString

• Multiplicity: [0..1]

beginLifespanVersion «lifeCycleInfo»

Date and time at which this version of the spatial object was inserted or changed in the spatial data set.

• Attribute name: beginLifespanVersion

• Type: DateTime

• Multiplicity: [1]

reasonForChange

The cause of the creation of the current version of the feature.

• Attribute name: reasonForChange

• Type: ReasonForChangeValue

• Multiplicity: [1]

form «voidable»

The nature of the watercourse being represented by the feature.

• Attribute name: form

• Type: WatercourseFormValue

• Multiplicity: [1]

level «voidable»

A description of the relationship of the watercourse to ground level.

• Attribute name: level

• Type: VerticalPositionValue

• Multiplicity: [1]

provenance

The origin of the centrelineGeometry property.

• Attribute name: provenance

• Type: WatercourseProvenanceValue

• Multiplicity: [1]

flowDirection «voidable»

Direction of water flow in the segment relative to digitisation of segment geometry.

• Attribute name: flowDirection

• Type: LinkDirectionValue

• Multiplicity: [1]

primacy

Value indicating the relative importance of the WatercourseLink within any larger watercourse it is part of.

• Attribute name: primacy

• Type: Integer

• Multiplicity: [1]

watercourseNumber

The code assigned by a responsible body that is used to identify the watercourse. The responsible bodies are Environment Agency for England, the Scottish Environmental Protection Agency for Scotland, and Natural Resources Wales for Wales. Not currently populated.

• Attribute name: watercourseNumber

• Type: CharacterString

• Multiplicity: [0..1]

watercourseName

The name of the watercourse that the WatercourseLink is part of.

• Attribute name: watercourseName

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

watercourseNameAlternative

An alternative name of the watercourse that the WatercourseLink is part of.

• Attribute name: watercourseNameAlternative

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

localName

A name that applies to part of a watercourse that is a sub-section of a larger named watercourse that the WatercourseLink is part of.

• Attribute name: localName

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

localNameAlternative

An alternative name that applies to part of a watercourse that is a sub-section of a larger named watercourse that the WatercourseLink is part of.

• Attribute name: localNameAlternative

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

catchmentName

The name of the catchment area where the WatercourseLink falls, assigned by a responsible body. The responsible bodies are Environment Agency for England, the Scottish Environmental Protection Agency for Scotland, and Natural Resources Wales for Wales.

• Attribute name: catchmentName

• Type: CharacterString

• Multiplicity: [0..1]

catchmentID

The code of the catchment area where the WatercourseLink falls, assigned by a responsible body. The responsible bodies are Environment Agency for England, the Scottish Environmental Protection Agency for Scotland, and Natural Resources Wales for Wales.

• Attribute name: catchmentID

• Type: CharacterString

• Multiplicity: [0..1]

permanence

A logical indicator that describes if the watercourse contains water year-round (in normal conditions) or only contains water intermittently. For example, a flood relief channel would have this set to ‘False’.

• Attribute name: permanence

• Type: Boolean

• Multiplicity: [1]

managedNavigation

A logical indicator that describes whether the watercourse is managed for inland navigation by a member of The Association of Inland Navigation Authorities (AINA). All values are currently set to false, future releases of the product may include values set to true.

• Attribute name: managedNavigation

• Type: Boolean

• Multiplicity: [1]

length

Calculated two-dimensional length of network segment in metres. Value supplied to one decimal place.

• Attribute name: length

• Type: Length

• Multiplicity: [1]

gradient «voidable»

A calculated percentage value that indicates the rate of descent of the surface of the water. See Gradient for derivation. Where the gradient does not correlate with the flow, this value is not supplied and a “nilReason” of ‘unknown’ is given.

• Attribute name: gradient

• Type: Real

• Multiplicity: [1]

width «voidable»

The average width of the watercourse along the WatercourseLink expressed in metres. This value is void for WatercourseLink features derived from Ordnance Survey large-scales single line features. These values will be given a “nilReason” of ‘unknown’.

• Attribute name: width

• Type: Distance

• Multiplicity: [1]

levelOfDetail

A calculated value indicating the relative cartographic importance of a WatercourseLink to aid selection and depiction when styling the data. See LevelOfDetail for derivation.

• Attribute name: levelOfDetail

• Type: LevelOfDetailValue

• Multiplicity: [0..1]

HydroNode features explicitly represent the starts, ends and junctions of watercourses, and places where certain attribution changes. They only exist at the end points of the WatercourseLink features. HydroNode positions are provided in 3D. The vertical coordinate has been sourced from Ordnance Survey terrain data.

HydroNode attributes

HydroNode

Definition: A feature at the end of one or more WatercourseLink features that indicates the confluence of two or more watercourses and / or a change in attribution of the connected WatercourseLink features.

• Subtype of: HydroNode

reasonForChange

The cause of the creation of the current version of the feature.

• Attribute name: reasonForChange

• Type: ReasonForChangeValue

• Multiplicity: [1]

geometry

The location of the HydroNode.

• Attribute name: geometry

• Type: GM_Point

• Multiplicity: [1]

inspireId

External object identifier of the spatial object.

• Attribute name: inspireId

versionId «lifeCycleInfo»

The identifier of the particular version of the spatial object, with a maximum length of 25 characters. If the specification of a spatial object type with an external object identifier includes life-cycle information, the version identifier is used to distinguish between the different versions of a spatial object. Within the set of all versions of a spatial object, the version identifier is unique.

• Attribute name: versionId

• Type: CharacterString

• Multiplicity: [0..1]

beginLifespanVersion «lifeCycleInfo»

Date and time at which this version of the spatial object was inserted or changed in the spatial data set.

• Attribute name: beginLifespanVersion

• Type: DateTime

• Multiplicity: [1]

hydroNodeCategory «voidable»

Nature of the HydroNode.

• Attribute name: hydroNodeCategory

• Type: HydroNodeCategoryValue

• Multiplicity: [1]

This section describes the structured data types which make up OS MasterMap Water Network Layer. The attributes associated with the data types are listed on the following two pages. The following information is given for each attribute.

Structured data type attribute information

Name and Definition

The name of the attribute and what it is describing.

Data type

The nature of the attribute, for example, a numeric value or a code list value.

Multiplicity

Describes how many times this element is expected to be populated in the data. An attribute may be optional or mandatory within the product. These are denoted by:

• ‘1’ – there must be a value.

• ‘0..1’ – population is optional but a maximum of one attribute will be returned. These values may be used in combination.

The linearReference data type will be used where required to record interaction over a length of a WatercourseLink. For example, linear interactions could be used to record where the water network passes under the bridge for a distance at A, over a weir at B or has an associated fish pass at an offset at C.

Where a linear interaction applies to two or more links, then each part of the interaction is recorded by means of more than one networkReference property.

LinearReference attributes

Reference to a part of a WatercourseLink along which a specific property applies.

• Subtype of: SimpleLinearReference

fromPositionGeometry

Point geometry to explicitly locate the start location from which the property applies.

• Attribute name: fromPositionGeometry

• Type: GM_Point

• Multiplicity: [1]

toPositionGeometry

Point geometry to explicitly locate the end location to which the property applies.

• Attribute name: toPositionGeometry

• Type: GM_Point

• Multiplicity: [1]

The pointReference data types will be used to record interactions at points on the WatercourseLink (interactions with a length of less than 2 m). For example, point interactions could be used to record the presence and position of features such as sluices.

PointReference attributes

Reference to specific point on a WatercourseLink at which a specific property applies.

• Subtype of: SimplePointReference

atPositionGeometry

Point geometry to explicitly locate where on the WatercourseLink the property applies.

• Attribute name: atPositionGeometry

• Type: GM_Point

• Multiplicity: [1]

A code list or enumeration is a controlled set of values which can be used to populate a specific column.

The following pages contain the code lists / enumerations used by OS MasterMap Water Network Layer:

Code list: LinkDirectionValue

List of values for flow relative to a WatercourseLink coordinate order http://inspire.ec.europa.eu/codelist/LinkDirectionValue/

Where the flow direction has not been determined, this attribute is set to null and a ‘nilReason’ is given.

• Where the value of nilReason is set to ‘unknown’, then the flow direction is not known to Ordnance Survey. A correct value may exist, but the methods employed by Ordnance Survey to date have not facilitated capture.

• Where the value of nilReason is set to ‘missing’, then the flow can be considered indiscernible. Ordnance Survey has attempted to identify the flow on the ground, but no flow has been determined.

codeList: WatercourseFormValue

Classification value defining the type of WatercourseLink.

Where the WatercourseForm has not been determined, this attribute is set to 'null' and the value of nilReason is set to ‘unknown’.

codeList: WatercourseProvenanceValue

The source and/or technique used to create the WatercourseLink feature.

A feature may have been obtained from more than one source; where this is the case, the following priority order is used to assign the provenance value:

1. OS-line or OS-area

2. localAuthoritySurveyed or nationalAuthoritySurveyed

3. localAuthorityInferred or nationalAuthorityInferred

4. inferred

Code List: LevelOfDetailValue

This attribute is currently set to a single value of ‘Local’, pending future developments in creating an attribute set in sympathy with OS Open Rivers data.

A calculated value indicating the relative cartographic importance of a WatercourseLink to aid selection and depiction when styling the data.

Code list:ReasonForChangeValue

The relative vertical position of a feature.

Where the VerticalPosition has not been determined, this attribute is empty, with a nilReason explicitly stated as ‘unknown’. A correct value does exist, but the methods employed by Ordnance Survey to date have not facilitated capture.

Code list: HydroNodeCategoryValue

Classification value defining the type of hydrographic node.

Where the hydroNodeCategory has not been determined, this attribute is set to null and the value of nilReason is set to ‘unknown’.

codeList: WatercourseTypeValue

Classification value defining the type of Watercourse.

The following three feature types are not currently populated in the current version of OS MasterMap Water Network Layer:

• WatercourseSeparatedCrossing

• WatercourseLinkSet

• WatercourseInteraction

However, these three feature types are referenced in the product’s schema, which is the controlling specification for the product. The intention is to add these three feature types into future versions of the product.

A feature used to indicate the relationship between watercourses that pass over one another without interaction. The WatercourseLink features are not broken at these locations, and the WaterCourseSeparatedCrossing feature is used to describe the vertical sequence of WatercourseLink features.

WatercourseSeparatedCrossing

A feature that indicates two or more watercourses which pass over one another at different physical levels.

• Subtype of: WatercourseSeparatedCrossing

element

Sequence of crossing links. The order reflects their elevation; the first WatercourseLink is the lower WatercourseLink.

• Association Role: element

• Multiplicity: [2..*]

reasonForChange

Reason for the current version to be created

• Attribute name: reasonForChange

• Type: ReasonForChangeValue

• Multiplicity: [1]

geometry

Point where two or more WatercourseLink features intersect.

• Attribute name: geometry

• Type: GM_Point

• Multiplicity: [1]

This spatial object type is included for future use to record sets of links that when combined create a recognisable identifiable watercourse, for example, a named river or a canal.

WatercourseLinkSet

A feature recording a set of watercourse links representing an identifiable watercourse.

• Subtype of: LinkSet

reasonForChange

The cause of the creation of the current version of the feature.

• Attribute name: reasonForChange

• Type: ReasonForChangeValue

• Multiplicity: [1]

watercourseNumber

Official code assigned to identify the watercourse. This is an official identification code assigned by a responsible authority, such as the Environment Agency (EA) or the Scottish Environmental Protection Agency (SEPA).

• Attribute name: watercourseNumber

• Type: CharacterString

• Multiplicity: [0..1]

watercourseName

The name of the watercourse that the WatercourseLinkSet is representing.

• Attribute name: watercourseName

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

watercourseNameAlternative

An alternative name of the watercourse that the WatercourseLinkSet is representing.

• Attribute name: watercourseNameAlternative

• Type: LocalisedCharacterString

• Multiplicity: [0..1]

watercourseType

The type of watercourse that the WatercourseLinkSet represents.

• Attribute name: watercourseType

• Type: WatercourseTypeValue

• Multiplicity: [1]

A feature that allows the supply of additional information related to the network in addition to the attribution and geometry of WatercourseLink features. For example, where a watercourse passes under a bridge or over a weir.

WatercourseInteraction

A feature that describes an event along a watercourse related to the water network that cannot be indicated by the attribution or geometry of the WatercourseLink or HydroNode feature(s).

• Subtype of: NetworkProperty

reasonForChange

Reason for the current version to be created.

• Attribute name: reasonForChange

• Type: ReasonForChangeValue

• Multiplicity: [1]

watercourseInteractionCategory

Not currently populated in OS MasterMap Water Network Layer.

• Attribute name: watercourseInteractionCategory

• Type: HydroNodeCategoryValue

• Multiplicity: [1]

Interactions can be either PointReference (for interactions less than 2m in length) or LinearReference (for interactions more than 2m in length). These record the position along a specified WatercourseLink for a point interaction, or the start and end position along one or more links for a linear interaction.

Interactions can be recorded with an offset indicating which side of the WatercourseLink the interaction is and a distance.

Simple Features – Level 1

The Geography Markup Language (GML) data conforms to GML Simple Features Profile Level 1. In this release of the product, the only thing that does not conform to level 0 is the inspireId.

The geometries that we use are OGC ‘simple’: points, and line strings with linear interpolation.

Schemas

XML schemas are used to define and validate the format and content of the GML. The GML 3.2.1 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 Ordnance Survey application schema waterNetwork.xsd, which is referenced by the data, is available on our website. It imports the INSPIRE Hydrography networks application schema, which in turn imports the GML 3.2.1 schemas. These in turn import schemas produced by the W3C. The data contains elements and attributes from a range of namespaces:

The XML namespaces used by the application schema and their definitions:

OS MasterMap Water Network Layer is supplied as a single GeoPackage for the whole of Great Britain. GeoPackage (*.gpkg) is an open, non-proprietary, platform-independent, standards-based data format for geographic information systems (GIS), as defined by the Open Geospatial Consortium (OGC). It is designed to be a lightweight format that can contain large amounts of varied and complex data in a single, easy-to-distribute and ready-to-use file. GeoPackage is natively supported by numerous software applications.

GeoPackage offers users the following benefits:

• The single file is easy to transfer and offers the end-user a rich experience.

• Attribute names are not limited in length, making the format user-friendly.

• The file size limit is very large at 140TB (A file size limit might be imposed by the file system to which the file is written).

• It supports raster, vector and database formats, making it a highly versatile solution.

• It is an OGC standard.

• In most cases, it is a plug-and-play format.

For information on how to open, use and understand a GeoPackage dataset, please refer to our ‘Getting Started with GeoPackage’ guide. Further detailed information on GeoPackage can be taken from the GeoPackage website.

Attribute naming differences between GML and GeoPackage formats

The naming of attributes between GeoPackage and the Geography Markup Language (GML) file is very similar as GeoPackage files are not limited in the number of characters for an attribute name. Therefore, the tables included here map the GML attribute name to the attribute name in the GeoPackage files.

The GML contains an attribute which describes the geometry of the feature; this is not applicable for a GeoPackage file as they are separated by their geometry.

Please note that the use of an asterisk symbol (*) in the following tables indicates that a particular attribute is not mapped to GML.

WatercourseLink

HydroNode

OS MasterMap Water Network Layer is supplied as a national vector tiles set in a single MBTiles file. This is a lightweight set of tiles that are efficient and fast to render in your software, and which provide high- resolution data and give a seamless experience when zooming in and out. The data is supplied in Web Mercator projection (ESPG:3857).

Vector tiles schema

The vector tiles schema is detailed in the following table. In the zoom levels columns within the table, the letter N indicates that the specified layer and attribute are not mapped within that zoom level, whereas the letter Y indicates that the specified later and attribute are mapped within that zoom level.

Watercourse_link layer

hydro_node layer

Attribute naming differences between GML and vector tiles formats

The naming of attributes between vector tiles and the Geography Markup Language (GML) file is very similar as the vector tiles set within the MBTiles file is not limited in the number of characters for an attribute name.

WatercourseLink

The following table maps the GML attribute name to the attribute name in the vector tiles for WatercourseLink:

HydroNode

The following table maps the GML attribute name to the attribute name in the vector tiles for HydroNode:

Data creation

Data was created from Ordnance Survey large-scale data with additional input from recognised bodies.

In OS MasterMap Topography Layer, watercourses with less than specified widths are captured as single line features for cartographic clarity purposes. These dimensions are 1m in urban areas, 2m in rural areas and 5m in mountain and moorland areas.

For watercourses captured as area features, algorithms were used to create a network, including generating topological connections if appropriate. Additional connecting geometry has been added to ensure topological connectivity where this can be deduced by inspection.

Watercourses represented by line features were used to generate network lines and these were extended both automatically and manually to indicate connectivity.

Manual improvement was undertaken where validation identified issues with flow and connectivity, and as a result of customer feedback.

Derived attributes

This section describes how attributes are derived from other information contained within Ordnance Survey large-scale data.

Width attribute

The width attribute is calculated to provide an average width of the Topographic Area feature(s) used to create the network links. There may be significant variation along the portion of the watercourse represented by a WatercourseLink with a single width attribute.

Topographic line and area features

The majority of links in the data were sourced from Ordnance Survey detailed topographic data. Different depictions within Ordnance Survey detailed topographic data are adopted for cartographic clarity purposes, and watercourses may be represented as lines or areas. Watercourses with less than specified widths are captured as single line features, while watercourses with greater than specified widths are captured as area features.

Parameters used by OS for topographic line and area features on watercourses:

Advances in data capture techniques mean that the cartographic constraints on capture as area features are now less pronounced. As a result, some features below the minimum widths in the table above may have been captured as areas.

LevelOfDetail

This is a calculated value indicating the relative cartographic importance of a WatercourseLink to aid selection and depiction when styling the data. Currently, this has been populated with a single value pending the development of algorithms to create more usable attribution.

Primacy attribute

The Primacy attribute is derived by assessing a combination of the flow, width, gradient and length of the network WatercourseLink feature to identify the most likely course of the main flow of a watercourse at bifurcations.

Gradient attribute

Gradient is a calculated attribute that indicates the rate of descent of the surface of the water over the entire length of the WatercourseLink.

Gradient is expressed as a percentage or drop in metres per 100metres of WatercourseLink length.

Gradient = (Height on first vertex – Height on last vertex * 100) / Planar length of link

For more detailed analysis of the WatercourseLink, height is provided on each vertex that can allow a user to calculate gradients within sections of the WatercourseLink.

Heighting the network

The water network was heighted by interpolation from a bare earth terrain comprising mass points and breaklines. The highest resolution height information available was used in this process. This terrain was captured by Ordnance Survey recently and is the basis for new products that include a height component.

The data used to height the network is of a resolution and quality that in some cases results in height attribution that contradicts the flow attribution. This is typically in areas with little change in elevation. In these cases, the calculated gradient attribute will not be supplied.

Future developments will reduce occurrences by improving the terrain data to reflect the influence of watercourses on the terrain surface.

Further information about the product can be found on:

• The OS MasterMap Water Network Layer product page on the OS website

• The OS MasterMap Water Network Layer Overview

• The OS MasterMap Water Network Layer Getting Started Guide

Loading the data in GeoPackage and vector tiles formats

The product's Getting Started Guide focuses solely on using the product in Geography Markup Language (GML) format. For guidance on using the product in GeoPackage or vector tiles formats, please see either the Getting Started with GeoPackage guide or the Getting Started with Vector Tiles guide.