> 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/buildings-and-infrastructure-portfolio/os-mastermap-topography-layer-building-height-attribute/os-mastermap-topography-layer-building-height-attribute-technical-specification/feature-type/building-height-attribute.md).

# Building Height Attribute

## Feature type attributes

### OS\_TOPO\_TOID

Unique feature identifier of the topographicArea building polygon taken from OS MasterMap Topography Layer.

* **Type:** CharacterString
* **Length:** 20
* **Multiplicity:** \[1]

### OS\_TOPO\_TOID\_VERSION

The version number of the TOID for which the height values have been calculated.

* **Type:** Integer
* **Length:** 3
* **Multiplicity:** \[1]

### BHA\_ProcessDate

The date that the Building Height Attribute values were calculated for the given OS\_TOPO\_TOID. Dates will follow the structure YYYY-MM-DD.

* **Type:** Date
* **Length:** 10
* **Multiplicity:** \[1]

### TileRef

The 5km² tile reference within which the Building Height Attribute is located.

* **Type:** CharacterString
* **Length:** 6
* **Multiplicity:** \[1]

### AbsHMin

AbsHMin is the absolute minimum height of the intersection of the external building walls and the underlying ground surface.

* **Type:** Real
* **Length:** 4.1
* **Multiplicity:** \[1]

### AbsH2

AbsH2 is the absolute height of the base of the roof, that is, where the roof intersects the principal part of the building. The principal part of the building is defined as the main structure.

* **Type:** Real
* **Length:** 4.1
* **Multiplicity:** \[0..1]

### AbsHMax

AbsHMax is the absolute height of the highest point on the building and can include any structure, such as chimneys, plant housings and machinery.

* **Type:** Real
* **Length:** 4.1
* **Multiplicity:** \[0..1]

### RelH2

RelH2 = AbsH2 – AbsHMin. RelH2 is the relative building height from the base of the building (AbsHMin) to the height of the base of the roof (AbsH2).

* **Type:** Real
* **Length:** 4.1
* **Multiplicity:** \[0..1]

### RelHMax

RelHMax = AbsHMax – AbsHMin. RelHMax is the relative building height from the base of the building (AbsHMin) to the height of the highest point on the building (AbsHMax).

* **Type:** Real
* **Length:** 4.1
* **Multiplicity:** \[0..1]

### BHA\_Conf

A qualitative assessment of the confidence of the height statistics for each topographicArea building polygon.

* **Type:** BHA\_ConfValue
* **Length:** 2
* **Multiplicity:** \[1]


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