# OS Open TOID Overview

OS Open TOID is an open dataset of unique identifiers – Topographic Identifiers (TOIDs) – assigned by OS to real-world features extracted from the following three OS MasterMap products:

* [OS MasterMap Topography Layer](broken://pages/86t0HHw73LlkkeXCGJSv)
  * TopographicArea
  * TopographicLine
  * TopographicPoint
* [OS MasterMap Sites Layer](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer.md)
  * SiteExtent
* [OS MasterMap Highways Network – Roads](/os-downloads/products/transport-network-portfolio/os-mastermap-highways-network-roads.md)
  * RoadNode
  * RoadLink
  * PathLink

This product allows users to share and link information related to a wide range of landscape and built environment features with a unique identifier and generalised location which will allow them to be used easily by everyone.

{% hint style="info" %}
TOIDs are unique and persistent identifiers, assigned by OS, for real-world features that have a physical presence in the world around you, such as a building or a road. A TOID consists of the letters ‘osgb’ and either 13 or 16 digits between 0 and 9. The TOID is allocated sequentially when a feature is created by Ordnance Survey and is never reassigned to a different feature. 

For the TOID to be fully effective, it is essential that the OS-appointed TOID reference is not altered in any way.
{% endhint %}

OS Open TOID provides the identifiers for these features along with their generalised location:

* **Point features**: The original location rounded to the nearest metre.
* **Line features**: The midpoint of the line rounded to the nearest metre.
* **Polygons features**: Use a point of inaccessibility algorithm to find a point that is guaranteed to be within the polygon which is farthest from all edges; this location is then rounded to the nearest metre.
* **Multi-polygon features (SiteExtent)**: Use the same method as for polygon features on the largest of the polygons.

<figure><img src="/files/HUKxEtxlkUMeiSqm3MkJ" alt="Visualisation of OS Open TOID data showing three unique features and their associated metadata." width="563"><figcaption><p>Visualisation of OS Open TOID data showing three unique features and their associated metadata.</p></figcaption></figure>

## Key features <a href="#bookmark23" id="bookmark23"></a>

The key features of the OS Open TOID product are:

* The comprehensive inclusion of all Ordnance Survey’s capture of the physical features across Great Britain.
* Access to our unique topographic identifiers, allowing you to link to the OS MasterMap products.
* A guide to which products the features are sourced from.
* The ability to reference between a feature and qualitative data using a unique identifier.

## Product applications <a href="#bookmark22" id="bookmark22"></a>

OS Open TOID offers a range of opportunities to link and share disparate datasets against a unique identifier, with a location.

For example, a local authority may use OS Open TOID to link unaddressed buildings captured within OS MasterMap Topography Layer with information such as ownership or planning permission to build a richer picture of land and property in their remit.

OS Open TOID is a dataset that is designed to use the OS MasterMap product family as a basis with which you can create your own rich, comprehensive dataset that caters to your specific needs. It is not designed to be used as a geospatial selector for features.

<figure><img src="/files/yvGEsfxQuohkTwTfYxQo" alt="Visualisation of OS Open TOID data showing three unique road node features and their associated metadata." width="563"><figcaption><p>Visualisation of OS Open TOID data showing three unique road node features and their associated metadata.</p></figcaption></figure>

## Index <a href="#index" id="index"></a>

This overview includes the following sections:

* [What is an identifier?](/os-downloads/products/buildings-and-infrastructure-portfolio/os-open-linked-identifiers/os-open-linked-identifiers-overview/what-is-an-identifier.md)
* [Product supply](/os-downloads/products/buildings-and-infrastructure-portfolio/os-open-toid/os-open-toid-overview/product-supply.md)
* [Coordinate reference system](/os-downloads/products/buildings-and-infrastructure-portfolio/os-open-toid/os-open-toid-overview/coordinate-reference-system.md)


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