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.
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.
A Guide to Coordinate Systems in Great Britain is available on the OS website.
Geography Markup Language (GML) 3.2.1, zipped using gzip
GeoPackage file, zipped using gzip
Vector tiles (MBTiles) file, zipped using gzip
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.
For GML, OS MasterMap Water Network Layer is a national dataset and is maintained and supplied as 5 km by 5 km 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 1.8 Gb zipped for GeoPackage and 1.5 Gb zipped for vector tiles.
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.
The customer submits an area of interest (AOI).
The online system creates a grid covering the entire area based on specified size; any 5 km by 5 km chunk that intersects the AOI will be included in the order.
Each square grid forms a chunk file.
Each feature that intersects that square goes into the chunk file.
OS MasterMap Water Network Layer is supplied in 5 km by 5 km 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.
OS MasterMap Water Network Layer change is 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.
This 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.
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.
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.
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:
Tracking water flows and contamination.
Flood prediction, protection and response measures.
Analytics and visual interpretation, particularly when used in combination with other Ordnance Survey products, for example, OS Terrain 5.
The management of statutory directives relating to watercourses.
Ecology studies, for example, species migration.
OS MasterMap Water Network Layer is supplied to customers quarterly in January, April, July and October, incorporating any updates made by the revision programme.
The product's Getting Started Guide focuses solely on using the product in Geography Markup Language (GML) format.
The product's Getting Started Guide focuses solely on using the product in GML format.
For guidance on using the product in GeoPackage format, please see theGetting started with GeoPackage guide.
For guidance on using the product in vector tiles format, please see the Getting Started with Vector Tiles guide.
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 product's Technical Specification, which is available on the OS website. The product has two core feature types: WatercourseLink and HydroNode.
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.
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.
