OS NGD Water Features

A Lightning Talk

What are the layers in OS NGD Water Features?

There are six feature types in the OS NGD Water Features collection: Water, Tidal Boundary, Intertidal Line, Water Point, Water Body Catchments and River Basin Districts.

Water

This is a set of water polygons, the same as the polygons in the Water theme in OS MasterMap Topography Layer. Water features shown as lines in OS MasterMap Topography Layer are not included in this data but can be extracted from the OS NGD Water Network.

Tidal Boundary

This contains Mean High Water and Mean Low Water lines as an unbroken dataset around the coast.

Intertidal Line

These are new linear features that would only be visible at low tide between the high and low water marks. Features such as watercourses and spreads

Water Point

These are water features at a specific location best represented as a point such as issues, sinks and culvert entrance.

Water Body Catchments

These are river catchments published by authoritative bodies. Where there is a long river they are broken into sections.

River Basin Districts

These are the macro river basins published by authoritative bodies named by region (South West, Anglian) or for the major river that runs through it (Humber, Severn).

Tidal Boundary

Although the geometry for the Tidal Boundary feature type is not new, the way it has been brought together is.

OS MasterMap Topography Layer represented MHW(S) and MLW(S) as two feature types. However, if the waterline was also a building, that would take precedence.

In this data all of the tide lines are in one layer and they are attributed as to what tide line they show (upper image)

• Mean High Water (Springs)

• Mean Low Water (Springs)

• Mean High and Low Water (Springs)

The data is also attributed to show what the feature forming the tide line is (lower image):

• Building Wall

• Built Obstruction

• Fixed Structure

• Lock Gate

• No Physical Feature (as you would expect on a beach)

Intertidal features

Intertidal lines are a new feature in OS NGD Data and represent features that exist between Mean High and Mean Low Water (Springs).

These features have been present in the OS database that sits behind products and are being exposed to users for the first time as part of the OS NGD data

The only two classifications are:

• Watercourse: where a stream runs across the foreshore

• Spreads: where a watercourse dissipates on the shoreline

Tidal Water

Another new feature of the OS NGD Water Features is the inclusion of Tidal Water polygons.

With OS MasterMap Topography Layer, ‘sea’ polygons stopped at the last point at which a feature broke the water polygon before it entered open sea with no bounding features. This would mean that tidal water often stopped at bridges with a blank on the seaward side.

Although the new Tidal Water polygons extend further out into the sea they do not extend to a fixed distance off shore all the way around the coast. Instead they extend out to the limit of the grid that Ordnance Survey has used to define the extent of Great Britain that it captures.

This means that missing squares in the middle of an area of sea polygons is because that square has no ‘land-based’ detail in it (coastline, islands, and so on) so Ordnance Survey has never produced data for it.

Water Body Catchments and River Basin Districts

Water Body catchment polygons are new to Ordnance Survey data and represent whole or part of a stream, river, lake, reservoir, estuary or stretch of coastal water

River Basin Districts are a river basin or several river basins together with associated coastal waters. This is the least-detailed level of catchment published by authoritative bodies.

Some of these districts relate to the widest catchments of specific rivers (Solway/Tweed, Dee, Severn, Thames, Humber) others are more regions or partial countries (South West, South East, North West, Anglian, Northumbria, Western Wales, Scotland).

The data has come from the relevant authoritative bodies:

• Environment Agency (England)

• Natural Resources Wales (Wales)

• Scottish Environment Protection Agency (Scotland)

What formats does the OS NGD Water data come in?

The OS NGD Water data comes in two formats, CSV and GeoPackage (GPKG)

• The GeoPackage format comes ready to load into the GIS package of the users choice with different gpkg files for each layer.

• The CSV format is more suited for loading into a database. It has all of the same layers in csv format and all the same attribution as the GeoPackage, however instead of storing the geometry in a GIS ready format, it is stored as a POLYGON, POINT, LINESTRING or MULTILINESTRING attribute with all of the vertices stored as co-ordinate pairs in the text file

What is the new attribution?

OS surveyors and remote sensing teams have been capturing and maintaining information on land cover, land use and a more detailed level of description for over 10 years.

This data has been transformed and filtered to match attribution and content for existing products, such as OS MasterMap Topography Layer. However, in the OS NGD data it is being published at the original, more granular level.

The attribution has changed from the OSMM Topography Layer:

• OS NGD data has an OSID

• The features have a TOID, version date and changetype similar to the OS MasterMap family of products, although the TOID is an optional field

• Land Use and Land Cover information has been added as well as a more detailed Description attribute. The Land Use contains a large amount of ‘Unknown’, but this is due to the nature of the features being water

Attribution across all of the Water Features (click on the image to enlarge it)

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Links that may be useful:

OS NGD Documentation Platform | osngd

OS Data HubOrdnanceSurvey

OS Select+Build | OS productsOrdnance Survey

This content has been developed from what was originally a Lightning Talk PowerPoint slide set. These slides are available to PSGA members to view and download from the PSGA members area of the OS website