Product supply

Available formats for the product

• 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 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.

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 5 km by 5 km 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 5 km by 5 km chunks.

Twelve chunks are created, one for every tile that is intersected by the area of interest (AOI).

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

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.