# Tram On Road Feature Type

## Background

The Tram On Road Feature Type can be found in the OS Transport Network Collection of the OS NGD Transport Theme. This feature type provides a stand-alone geometry to depict where tram tracks are on the road network. This geometry is derived from the Road Link Feature Type and as a result will be coincident with the Road Link features.

A Tram On Road feature is provided where a tram track is present on the road network. The feature represents the section of the Road Link where there is a tram track closely associated with it. When comparing this geometry to the Road Link Feature Type you would expect to find ‘gaps’ in Trams on Road features where tram tracks do not coincide with the entire Road Link.

All Tram On Road features have a linked identifier (Road Link ID attribute) to the Road Link feature they are associated with.

## Technical detail

The Tram On Road Feature Type aims to give a granular depiction of the where tram tracks exist on a Road Link.

To create the Tram On Road Feature Type, we have used an algorithm which assesses Railway Links, road surface polygons (part of the OS Transport Features Collection: Road Track Or Path topographic data) and Road Links.

The algorithm takes Railway Links with description value ‘Tram’ and applies a buffer to identify which road polygons intersect and are therefore closely associated with these tram links. All Road Links within the intersected polygons are then candidates for inclusion in the dataset. Further logic within the algorithm determines which Road Links are attributed with tram presence. A Tram on Road feature is created to indicate exactly where  the tram interacts closely with the Road Link, with its geometry derived from the Road Link.

Note that certain types of tram link are not considered by the algorithm, including 'preserved', 'static museum' and 'funicular'. These types of tram link are not required for transportation and navigation use cases, as they mainly serve a leisure purpose.

## Examples of uses this data supports

* Understanding where (the extents of) tram tracks are on the road network
* Visualisation of the physical extents of where tram tracks are on roads

<figure><img src="/files/2K1mDsgl3GBUFJvWxFMQ" alt="Example map showing the Tram On Road Feature Type. A background map has been included to provide context." width="563"><figcaption><p>Example map showing the Tram On Road Feature Type. A background map has been included to provide context.</p></figcaption></figure>

## Examples of uses this data doesn't support

* Routing along the tram network. Tram on Road consists of a discontinuous set of geometries, which is not a routable network. Instead, the [Railway Link Feature Type](/osngd/data-structure/transport/transport-network/railway-link.md) will help with this use case.
* A tram track centre line. Tram On Road uses Road Link geometry. The [Railway Link Feature Type ](/osngd/data-structure/transport/transport-network/railway-link.md)provides geometry for the generalised rail network, including tram tracks.


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