Theme definition

Description: The topological network representing driveable roads and vehicle ferries (not international routes) within Great Britain.

Theme rule: theme = ‘Road Network’

Features:

• Road
• RoadLink
• RoadNode
• FerryLink
• FerryNode
• FerryTerminal
• InformationPoint

Representation of the road network

The network is a representation of the real world, so the way roads are represented has to follow a set of rules to make sure that the depiction of roads is consistent throughout the product.

Road names and numbers

Named and numbered roads are captured in the Road Network theme as Road features. A Road feature represents a named or Department for Transport (DfT) numbered road, for example, Romsey Road or the A38. It may comprise one or more links and may also relate to links that are not connected (this occurs with some of the longer roads in Great Britain’s road network). This ensures all road links that comprise a single and discrete named or numbered road can always be related to its name or number, regardless of whether all the links connect. The Road feature includes information on the road type (named, motorway, A road or B road), the name or number, and a set of references to the RoadLink features that provide the network topology of the road.

The road name is collected by Ordnance Survey, usually during a ground visit. DfT road numbers are either based upon a ground visit or on information from the DfT.

A section of road that has both a name and number has two independent Road features, one for the name and one for the DfT number. Any single road link may be referenced by more than one Road feature; it may have both a road name and/or a road number, but it will not have two names or two numbers. For example, the A3057 and Romsey Road may both refer to at least some of the same links; however, an individual link would not be referenced to two numbered roads. An exception to this principle occurs for numbered roads that have sections classified as primary routes or trunk roads by the DfT. Unnamed and unnumbered roads are included as RoadLink features, but are not referenced by a Road feature.

A single RoadLink can have more than one road name; an example would be where a RoadLink has both an English and Welsh name.

Numbered roads

A Road feature representing a DfT numbered road references all of the RoadLink features that represent that classified road. These links may not be contiguous across junctions and, where a classified road consists of separate sections, they may be separated by some considerable distance.

Trunk roads and primary routes are captured as independent Road features with appropriate attribution. As they reference only the links that represent their geometry, this results in two numbered road references to the same link(s). In this case, the number will be the same but one feature will have an additional attribute describing it as a trunk road or primary route. Figure 1 illustrates this scenario.

Figure 1: A303 primary route joins the A30: the A30 then becomes a primary route.

In this example, three features are required:

• · The A30 representing all road links that are part of the A30
• · The A303 primary representing all road links that are part of the A303 primary route
• · The A30 primary representing the subset of the A30 that is classified as a primary route

Reference to RoadLinks by Road features representing DfT numbered roads at roundabouts and junctions

Any RoadLink may only be referenced by one DfT numbered road feature (with the exception of trunk roads and primary routes as described in the previous example). The following priorities are used to determine how links are referenced at road junctions, including roundabouts.

Ordnance Survey applies the road number from the DfT if the information is available for the link. If no information is available, a hierarchy is imposed by applying the following priorities:

1. Motorway
2. A trunk
3. A primary route
4. A road
5. B road

If two roads of equal magnitude meet, the lower numbered route is used. For example, the A1 trunk would be preferred over the A11 trunk. Figure 2 illustrates a scenario where numbered roads meet at a roundabout.

Figure 2: A33 has priority over A335 and A3024 at the roundabout: road links are referenced accordingly.

Named roads

A Road feature is created for each named road. As there are many roads with the same name (for example, High Street), a Road feature will be created referencing all the RoadLink features in a given area that represent a single named road.

In rare situations when a break in the RoadLink occurs, two (or more, depending on the nature of the break) different road name features will be created, both with the same name but referencing different links. Numbered roads reference every link that makes up their length.

Figure 3: The relationship between RoadLink and Road features

In figure 3, Crabwood Close is represented by a Road feature that references the RoadLink features 1, 2 and 3. This would be recorded as:

Road feature =   road name (Crabwood Close)

                        Network members:
                        1 = osgb4000000023313386
                        2 = osgb4000000023363738
                        3 = osgb4000000023363720 

Reference to RoadLink features by Road features representing named roads at roundabouts and junctions

At a roundabout or road junction, a RoadLink may only be referenced by one named Road feature. The following priorities determine how these links are referenced:

• Priorities reflect the real-world situation as far as possible.
• Where no single named road extends either side of a roundabout, the roundabout RoadLink features will not be referenced by any of the named Road features.
• If only one of the named roads extends either side, the roundabout RoadLink features will be referenced by that named Road feature.
• If more than one named road extends either side or crosses a roundabout, the named road that is coincident with any prioritised DfT numbered road feature will refer to the roundabout RoadLink features.
• If more than one named road extends either side of a roundabout and no DfT road numbering hierarchy exists, the RoadLink features may be referenced by one of the named road features if it can be identified as having more significance.
• If significance cannot be identified, the RoadLink features at a roundabout are not referenced by any Road feature.

Named roads at roundabouts

Figures 4 and 5 illustrate the application of priorities for named Road features at roundabouts.

Figure 4: Only Romsey Road (A3057) extends either side of the roundabout: the roundabout RoadLink features are named and referenced by the Romsey Road feature.

Figure 5: Stockbridge Road and Chichester By-pass extend either side of the roundabout. As the Chichester By-pass is coincident with the A27, which takes priority over the A286, the roundabout RoadLink features are named and referenced by the Chichester By-pass feature.

Named roads at junctions

Figure 6 illustrates the application of the priorities for named Road features at junctions.

Figure 6: High Street is identified as the continuous road and the RoadLink features are allocated accordingly. Green Lane is a single Road feature even though it is not a continuous road.

Road geometry

The general alignment of the road carriageway is represented by RoadLink features. RoadLink features include information about the geometry of the link, the type of road the link represents (for example, motorway or A road), and information about the nature of road the link represents (for example, single carriageway, dual carriageway or slip road). The length of the link and references to the node features at either end of the link are also included.

Grade separation information (identifying if one RoadLink is above another) is also included to indicate any restriction on accessibility from one link to another where they cross at bridges, flyovers and so on.

As the geometry of RoadLink features fall within the OS MasterMap Topography Layer polygons representing the road carriageway, RoadLinks include a reference to those polygon features in the OS MasterMap Topography Layer Roads, Tracks and Paths theme. In figure 7, a RoadLink (TOID osgb4000000023363433) lies within and references three OS MasterMap Topography Layer polygons (TOIDs osgb1000002109293982, osgb1000002109293983 and osgb1000002109115793).

Figure 7:  Reference between a RoadLink feature and topographic areas.

Road intersections

The road network is only broken in specific circumstances. Where this happens, a RoadNode feature is added coincident with the end of all relevant RoadLink features. The end of a RoadLink feature indicates one of the following situations:

• The intersection or crossing of carriageways (including bridges, flyovers and tunnels where there is no connectivity)
• The location where a road name or number changes
• The location where a road name or number ceases to apply
• The start or end of a carriageway
• If a section of a road between junctions is subject to a ‘one-way’ restriction, that section will be given a start and end node and becomes, in effect, a new link.

Each RoadNode feature is represented with point geometry and references the underlying polygon in the OS MasterMap Topography Layer.

Numbered motorway junctions

Each numbered motorway junction is currently represented as a single InformationPoint feature. Each point feature includes a representative location for the junction and details of the junction number and the roads intersecting at the junction. No other junctions are currently captured as discrete features.

Vehicular ferry routes

Vehicular ferry routes are comparable to the way in which the road network is represented and are represented by a combination of the following three features.

FerryLink

The existence of a vehicular ferry service is represented by a FerryLink. This feature does not have geometry itself but is a logical link between the locations where a ferry allows vehicles on and off. A ferry link feature necessarily includes references to the FerryNode features that represent its start and finish points; a straight line is inferred from these two nodes.

FerryNode

Each end of a FerryLink (this may indicate part of a ferry route for multi-stage services) is represented by a FerryNode. This feature represents the general location of the end of a FerryLink and has a single point position. A FerryNode feature may serve multiple FerryLink features if more than one destination is served from the same general location. 

FerryLink features do not have geometry of their own, so they cannot intersect in the way RoadLink features do. Therefore ferry node features only ever exist at a location where vehicles or people are permitted on and off the ferry.

FerryTerminal

The ferry and road networks are linked by a FerryTerminal feature, which represents where a potential change of mode of transport occurs from a road vehicle to ferry or vice versa. A FerryTerminal feature has no geometry but provides a logical link between the road and vehicular ferry networks.

In this section:

ITN Technical specification – home

Purpose of this specification

ITN network features

ITN data structure

Overview of ITN themes

ITN Road Network theme

ITN Road Routing Information (RRI) theme

ITN Urban Paths theme

ITN Path Routing Information (PRI) theme

ITN Layer qualifiers

Feature types and attribution in the Road Network theme

Feature types and attribution in the Road Routing Information theme

Feature types and attribution in the Urban Paths Network theme

Feature types and attribution in the Path Routing Information theme

Descriptions of ITN Layer attributes

Attribution checklists for the Road Network and Urban Paths Network themes

ITN attribute definitions and values

ITN GML output format

ITN Layer GML examples

ITN character set

ITN weights and width attribution

ITN steep gradient attribution

This web page is part of the technical specification for OS MasterMap^® Integrated Transport Network™ Layer. For the terms that apply to use of this specification, refer to Purpose of this specification.