> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/areas-and-zones-portfolio/os-open-built-up-areas/os-open-built-up-areas-overview/product-details.md).

# Product details

## Feature types <a href="#id-2.1-feature-types" id="id-2.1-feature-types"></a>

OS Open Built Up Areas is classified into three feature types: Built Up Areas, Built Up Extents, and

### Built Up Areas

Built Up Areas is the aggregation of Built Up Extents and Non Built Up Extents.

This is a multipart area feature with a single Government Statistical Service (GSS) code and name or names.

<figure><img src="/files/DfVCK53ROEtzWJ2Sslni" alt="A visualisation of the Built Up Extents and Non Built Up Extents Feature Types and attribution shown against a background map"><figcaption><p>Built Up Extents and Non Built Up Extents Feature Types and attribution.</p></figcaption></figure>

Full attribution for this feature type is available on the [Built Up Areas page of the technical specification.](/os-downloads/products/areas-and-zones-portfolio/os-open-built-up-areas/os-open-built-up-areas-technical-specification/feature-types/built-up-areas.md)

### Built Up Extents

Built Up Extents is the representation of built-up areas only within the extent of Built Up Areas. This is the area that remains after Non Built Up Extents have been removed from Built Up Areas.

This is a multipart area feature with the same GSS code as the related Built Up Areas with the same name or names.

{% columns %}
{% column %}

<figure><img src="/files/lEGY8T0wFTzDHj8htBOH" alt="A visualisation of the Built Up Extents Feature Type shown against a background map."><figcaption><p>Built Up Extents Feature Type.</p></figcaption></figure>
{% endcolumn %}

{% column %}

<figure><img src="/files/IlM94vdZzMjitCoR6g0R" alt="Example image showing the Built Up Extents Feature Type and attribution."><figcaption><p>Built Up Extents Feature Type and attribution.</p></figcaption></figure>
{% endcolumn %}
{% endcolumns %}

Full attribution for this feature type is available on the [Built Up Extents page of the technical specification.](/os-downloads/products/areas-and-zones-portfolio/os-open-built-up-areas/os-open-built-up-areas-technical-specification/feature-types/built-up-extents.md)

### Non Built Up Extents

Non Built Up Extents is the representation of non-built-up areas within the extent of Built Up Areas.

This is a multipart area feature with the same GSS code as the related Built Up Areas with the same name or names.

<figure><img src="/files/FsWYOlE8cm78dEwJWx6h" alt="A visualisation of the Non Built Up Extents Feature Type show against a background map"><figcaption><p>Non Built Up Extents Feature Type.</p></figcaption></figure>

Full attribution for this feature type is available on the [Non Built Up Extents page of the technical specification.](/os-downloads/products/areas-and-zones-portfolio/os-open-built-up-areas/os-open-built-up-areas-technical-specification/feature-types/non-built-up-extents.md)

## Standards <a href="#id-2.2-standards" id="id-2.2-standards"></a>

OS Open Built Up Areas is designed to conform to OGC standards.

## Coordinate reference system <a href="#id-2.3-coordinate-reference-system" id="id-2.3-coordinate-reference-system"></a>

OS Open Built Up Areas uses the British National Grid (BNG) coordinate reference system. BNG uses the OSGB36 geodetic datum and a single Transverse Mercator projection for the whole of Great Britain.

Positions on this projection are described using easting and northing coordinates in units of metres. The BNG is a horizontal spatial reference system only; it does not include a vertical (height) reference system.


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