OS NGD Structures

A Lightning Talk

What are the layers in OS NGD Structures?

There are five layers in OS NGD Structures. Four are shown here, the 5th is Field Boundaries covered separately.

Structure

Structure

These are features represented as areas like pylons, walls (historic), tanks, wells, solar panels, floating structures (like pontoons) and weirs that would have appeared in the Structures theme of OS MasterMap Topography Layer.

Structure Line

Structure Line

These are linear features such as built obstruction (known as obstructing feature in OS MasterMap Topography Layer), steps (now split into top, bottom, intermediate), tunnel walls (underpass, water, conduit, tube/metro), line of posts, sluice, gate, etc. that would have appeared in the Topographic Lines part of OS MasterMap Topography Layer.

Structure Point

Structure Point

These are features that were often Topographic Points in OS MasterMap Topography Layer such as post boxes, chimneys, electricity poles, posts, flag staffs, bollards and rail signal lights.

Compound Structure

Compound Structure

These are a new feature and comprise complex structures that often cross other features such as a road or river, represented as a single feature. Things like bridges (road, rail, swing, foot, transporter), viaducts, some sluices and underpasses.

Compound Structures

Definition: The new Compound Structure feature type is a polygon feature which encompasses one or more components and represents a manmade construction that has been built for a specific purpose. Examples include a bridge, a dam, and an aqueduct. A compound structure essentially combines multiple polygons into a single polygon, making it easier to analyse and query data.

Source: The data for these has been captured by OS Surveyors and the Remote Sensing team for a number of years but not released as part of formal products.

Considerations: These features are separate to the rest of the Structure polygons. They do not form part of a complete seamless ‘topographic’ layer of polygons (formed from features from Buildings, Land, Transport, Structures and Water themes) but sit above this as a collection of these polygons combined into single features.

Compound Structure Feature Type

What formats does the OS NGD Structures 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 MULTIPOLYGON, MULTIPOINT, LINESTRING or POLYGON attribute with all of the vertices stored as co-ordinate pairs in the text file.

What is the attribution?

The attribution varies between the feature types, but there are some common features:

• All OS NGD data has an OSID, version, version date and changetype

• Where the data has an ancestry from OS MasterMap there is a TOID, and where the data was present in the Building Heights Attribution, that data has come across for features in the Structure Feature Type such as Tanks, Chimneys and Glasshouses

• The data now has source, evidence and update dates so users can see where the information has come from and when it was updated

• There is also extra data around if the feature is obscured, tidal, historic, active and the specification it was captured to

Attribution example for a Glasshouse

Attribution across the four primary feature types of the Structures Features (click on the image to enlarge it)

Features with new attribution

Certain Structure feature types include a height attribute:

• Roofed Storage Tank

• Open Storage Tank

• Chimney

• Glasshouse

• Open Sludge Tank

NOTE: although these are the classifications that have height attributes, not all of the features in these classes have a height

Some Structure features do not include Land Use or Land cover attributes:

• Electricity Pylon

• Lighting Tower

• Telecommunications Mast

Features with height attribution

Bridge Attribution

Additional attribution = ‘networkover’ and ‘networkunder’ to the Bridge description has been added within the OS NGD Compound Structure on the following features:

Description = Aqueduct, Bridge, Clapper Bridge, Footbridge, Lift Bridge, Swing Bridge, Tanker Berthing, Transporter Bridge, Underpass, Viaduct, Footbridge

Description of the network passing over or under the bridge:

• Canal

• Multiple

• Path

• Railway

• Road

• Water

On rare occasions network over and network under cannot be identified (i.e., disused bridges or viaducts over dry valleys). In these cases these attributes will not be populated.

Where there are more than 1 network interactions with the structure, the description of multiple is applied, for example a road over rail and a river, over a river and a path.

As changes are made to the OS NGD layers including topographic features, Transport Network, Water Network and Structures features the bridge data is updated in this layer.

---

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