# Product data

## Data currency and completeness <a href="#bookmark17" id="bookmark17"></a>

Building Height Attribute data is derived from the latest source Digital Terrain Model (DTM) and Digital Surface Model (DSM).

## Header information <a href="#bookmark18" id="bookmark18"></a>

For the purposes of simplifying the merging process, the individual 5x5km² tiles are supplied without header information. Instructions on the merging process can be found in the [Getting Started Guide](https://docs.os.uk/os-downloads/products/buildings-and-infrastructure-portfolio/os-mastermap-topography-layer-building-height-attribute/os-mastermap-topography-layer-building-height-attribute-getting-started-guide).&#x20;

The format and structure of the individual columns within the data will be consistent (see table below).

### Building Height Attribute header information

<table data-header-hidden data-full-width="true"><thead><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td><strong>OS_Topo_ TOID</strong></td><td><strong>OS_Topo_TOID_ Version</strong></td><td><strong>BHA_Proces sDate</strong></td><td><strong>Tile Ref</strong></td><td><strong>AbsH Min</strong></td><td><strong>Abs H2</strong></td><td><strong>AbsH Max</strong></td><td><strong>Rel H2</strong></td><td><strong>RelH Max</strong></td><td><p><strong>BHA_</strong></p><p><strong>Conf</strong></p></td></tr></tbody></table>

The **Building Height Attribute header file** can be downloaded from the ['OS MasterMap Topography Layer – Building Height Attribute Downloads' page](https://docs.os.uk/os-downloads/products/buildings-and-infrastructure-portfolio/os-mastermap-topography-layer-building-height-attribute/os-mastermap-topography-layer-building-height-attribute-downloads).

## Data precision <a href="#bookmark19" id="bookmark19"></a>

All heights have been calculated in metres to one decimal place (decimetre).

## Height datum <a href="#bookmark20" id="bookmark20"></a>

The Building Height Attribute dataset uses Ordnance Datum Newlyn (ODN) as the national height datum for all height values across mainland Britain. Other British height datums (for example, Lerwick for the Shetland Islands) are used where applicable. All height datums are incorporated within the National Geoid Model OSGM15.

The following two guides can help you gain further insight into coordinate systems in Great Britain:

* [A Guide to Coordinate Systems in Great Britain ](https://docs.os.uk/more-than-maps/deep-dive/a-guide-to-coordinate-systems-in-great-britain)
* [Beginner's guide to grid references](https://getoutside.ordnancesurvey.co.uk/guides/beginners-guide-to-grid-references/)

<figure><img src="https://1897589978-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FcNpJpLP8RROUaWVQo5ea%2Fuploads%2FBdIC69voF5U0hiPWv0Tg%2F10.jpeg?alt=media" alt="Example image depicting OS MasterMap Topography Layer – Building Height Attribute displayed over OS Terrain 5 and OS MasterMap Imagery Layer." width="563"><figcaption><p><em>Image depicting OS MasterMap Topography Layer – Building Height Attribute displayed over OS Terrain 5 and OS MasterMap Imagery Layer.</em></p></figcaption></figure>