Ordnance Survey – Great Britain's national mapping agency
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What is the Integrated Transport Network Layer of OS MasterMap? |
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Will there be links from the ITN layer to the Local Street Gazetteer (LSG)? |
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What is the Integrated Transport Network Layer of OS MasterMap?
The OS MasterMap Integrated Transport Network (ITN) Layer is an accurate, detailed and up to date digital road network for Great Britain. It consists of two themes, Road Network and Road Routing Information. It provides a flexible foundation for publishing, tracking, routing, telematics, analysis and asset management solutions and can be fully integrated with all OS MasterMap layers, for example, Address Layer 2 for to the door routing.
How is the road network represented?
Individual sections of road are represented by RoadLink features, which show the general alignment of the carriageway. RoadLink features have attribution to describe the type and nature of the road.
RoadLink classifications include motorway, A road, B road, minor road, local street, private road - publicly accessible, private road - restricted access, alley and pedestrianised street. The nature of the road classifications includes single carriageway, dual carriageway, slip road, roundabout and traffic island.
RoadLink types
Dual carriageway, single carriageway, slip road, roundabout, traffic island, traffic island at junction, enclosed traffic area.
Ferry network
Ferry terminals, ferry link and ferry node.
The connectivity is described by relationships at the ends of the RoadLink features and a relative third dimension is included to allow for roads crossing at different levels.
Named and numbered roads are represented by compound features referencing the RoadLink features that represent the extent of the road.
How is Road Routing Information represented?
Information that may affect a driver's choice of route is represented by additional features that reference the base network. this is known as Road Routing Information (RRI). These features describe restrictions, permissions and other information relevant to drivers.
The routing information is not applied to the base network, but is referenced. This allows the range of information collected to be extended in the future and minimises the impact on customers not concerned with routing information.
The main categories of information captured are as follows:
One way, no entry, no turn, mandatory turns,access prohibited and access limited to (to whom the restrictions apply and any time constraints are also captured), height, width and weight restrictions, fords, mini roundabouts, traffic calming, gate, tolls, bridge over road, firing range, through route, severe turn.
Why is the road name not attributed to links?
Because a named or numbered road is a definable entity, the ITN layer considers it to be a discrete feature. The ITN layer adopts a relational structure for the data; RoadLink features describe each section in the road network and the road feature represents the named or numbered road. Every road feature will reference the TOID of one or more RoadLink features that represent the alignment of the road
Why doesn't the ferry link feature have any geometry?
The ferry link is provided to represent a ferry route by indicating that two ferry nodes are connected. It has no explicit geometry of its own because the precise route of a ferry is much more variable than a vehicle. Some software implementations will join the ferry nodes together which may result in a route that appears to pass over land.
How often is the ITN Layer updated?
It is updated when changes occurs to the Ordnance Survey large scale topographic data, information from DfT, Highways Agency, Highway Authorities and our own field surveyors. The aim is to include information in the OS MasterMap Topographic layer within 6 months of change occurring, ITN layer information, taken from the topographic layer, will be updated shortly after its publication in the topographic layer. A refresh is available to customers 6 weekly.
Are there polygons and networks in the ITN Layer?
The ITN Layer is primarily a topological network. There are also simple bounding rectangle polygons to indicate the extent of named and numbered roads.
Will there be links from the ITN layer to the Local Street Gazetteer (LSG)?
The structure of OS MasterMap allows for data association, therefore other datasets, such as LSG data, can be linked to the ITN layer TOID.
Some highway authorities have used the ITN layer to create a baseline LSG.
A paper is available explaining how to create a level 3 gazetteer using the ITN Layer.
What is the definition of public and private roads?
OS receives feedback from local authorities, generally via the Department for Transport, indicating if any roads need to be reclassified from public to private or vice versa. Where these do not clash with the OS specification such changes are incorporated.
Are settlement names in the data?
Settlement names are no longer included in the data. The 1:50 000 Scale Gazetteer, with many more names, can be used in conjunction with the ITN layer.
Are symbols available?
A generic set of symbols is available that can be adapted to suit individual use. >>
Are car parks included in the ITN layer?
Car parks and similar enclosed traffic areas that are accessed by identifiable roads will have their access roads captured and identified by its attribution. Internal routes within car parks will not be captured.
Is there a road centreline in the ITN Layer?
No, there is no road centreline. You can use the RoadLink features, but please bear in mind that these may not be in the exact centre of the road carriageway. They are indicative of the alignment only.
How many times does the road name appear in the data?
A road feature will occur once for each named road within a specific area in the road feature and is linked to the road link features that make up that road by reference to the constituent road link TOIDs. Numbered roads are created as single features, no matter how fragmented they are. For example, there are 1 017 occurrences of Green Lanes but only one B3181.
How many features are in the data?
Roads Network:
- 4 101 628 road links
- 3 445 935 road nodes
Road Routing Information features:
- 924 565
DfT numbered roads:
- Motorways 68
- A roads 2568
- B roads 3201
- Minor roads 722 790
Total length of GB roads: 545129.53km
[Statistics as of March 2009]
Other statistics
Most popular road name: High Street - 2 453 occurrences (Church Street, Church Lane and Station Road all occur more than 1 500 times).
Longest single road link: 20.3 km (alongside Loch Arraign, Scotland).
What is the data format for the OS MasterMap ITN Layer?
The data format is GML v2.1.2.
How much space does the ITN layer require?
514Mb unzipped (Road Network and RRI)
This demo gives a more detailed technical explanation of ITN
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