# What is an identifier?

Identifiers are vital to easily and uniquely identify something. For example, a blue Ford Fiesta is a very common car in Britain. Identifying one from another would be very difficult without using a license plate – one form of an identifier. The unique identifier is key to Automatic Number Plate Recognition (ANPR) for schemes such as electronic toll collection, traffic movement monitoring, and checking if a vehicle is taxed, insured and road safe.

Identifiers are the 'golden thread' linking data together and can be used to effectively retrieve, reuse, publish and link multiple datasets together. NHS Numbers are an example of an identifier being used as the 'golden thread' for our historic health and care record. Our name and address are highly changeable personal details and cannot be relied on in isolation to access our health and care record. But our NHS Number can be used by healthcare providers across all NHS services to correctly retrieve our health records and link them with other datasets, such as our hospital number.

There are many examples in our everyday lives where identifiers ensure that accurate and efficient decisions are made on reliable data.

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FguurxQAt1y8YwVFZGG4U%2F1.jpeg?alt=media" alt="Visualisation of USRN identifiers being used to uniquely identify two streets on a map. Two streets on the map are highlighted in yellow and have information listed for their USRN and street type attributes." width="563"><figcaption><p>Visualisation of USRN identifiers being used to uniquely identify two streets on a map.</p></figcaption></figure>

## What are the OS identifiers? <a href="#bookmark2" id="bookmark2"></a>

OS has three authoritative identifier schemes in its Download OpenData and Premium data products:

* **Topographic Identifier (TOID)** – For every feature in our large-scale geospatial database.
* **Unique Property Reference Number (UPRN)** – For every addressable location in Great Britain.
* **Unique Street Reference Number (USRN)** – For every street across Great Britain.

These identifiers can be found throughout our Premium datasets, including, but not limited to, [OS MasterMap Topography Layer](https://docs.os.uk/os-downloads/topography/os-mastermap-topography-layer), [OS MasterMap Highways Network](https://docs.os.uk/os-downloads/networks/os-mastermap-highways-network-fundamentals) and [AddressBase](https://docs.os.uk/os-downloads/addressing-and-location/addressbase) offerings.

This overview document introduces you to four OpenData products which include these identifiers, the so-called OS Open Identifiers 'Family' of products:

* [**OS Open Linked Identifiers**](https://docs.os.uk/os-downloads/identifiers/os-open-linked-identifiers): A dataset containing the relationship between UPRNs, USRNs and TOIDs. The relationships are extracted from the OS MasterMap Highways Networks Family of products and the AddressBase Premium product.
* [**OS Open TOID**](https://docs.os.uk/os-downloads/identifiers/os-open-toid): A dataset containing a generalised location for a wide range of features, such as buildings without an address, road junctions, land cover and more. These are extracted from OS MasterMap Premium products.
* [**OS Open UPRN**](https://docs.os.uk/os-downloads/identifiers/os-open-uprn): This includes UPRNs and geometry from AddressBase Premium, such as residential and commercial dwellings, ponds, electricity substations and advertising hoardings.
* [**OS Open USRN**](https://docs.os.uk/os-downloads/identifiers/os-open-usrn): This includes USRNs from the OS MasterMap Highways Network Family of products with a simplified line geometry.

## Background on the OS Open Identifiers Family of products <a href="#bookmark3" id="bookmark3"></a>

OS Open Identifiers is a family of OpenData products, including OS Open Linked Identifiers, OS Open TOID, OS Open UPRN and OS Open USRN . The products within this family allow you to easily share information held against a range of identifiers and to link together information associated with these identifiers.&#x20;

The OS Open Identifiers products have been created to support the use of the [OS Open Identifiers Policy](https://www.ordnancesurvey.co.uk/products/open-mastermap-programme/open-id-policy), which has been designed to remove barriers and allow organisations to publish more of their own data with OS identifiers, providing additional valuable data into the geospatial ecosystem.

{% hint style="success" %}
Using the OS Open Identifiers Family of products, you can:

* Easily share information held against a range of identifiers.
* Link together information associated with a range of identifiers.
  {% endhint %}

The relationship between these key identifiers can be obtained from the OS Open Linked Identifiers product. The product consists of 11 relationships, as shown in the diagram below. Each relationship is available to download individually from the [OS Data Hub](https://osdatahub.os.uk/data/downloads/open/Terrain50). Please refer to the [OS Open Linked Identifiers Overview](https://docs.os.uk/os-downloads/identifiers/os-open-linked-identifiers/os-open-linked-identifiers-overview) for further details.

<div align="center"><figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FeJ6BObHJJN3y02rM4Jyo%2F2.png?alt=media" alt="pen Linked Identifiers diagram showing the interconnected relationship in the product between TOIDs, UPRN, USRNs, and GUID." width="563"><figcaption><p>OS Open Linked Identifiers diagram showing the interconnected relationship in the product between TOIDs, UPRN, USRNs, and GUID.</p></figcaption></figure></div>
