OS MasterMap Topography Layer – Building Height Attribute is a dataset containing absolute and relative height values for buildings and selected structures contained within OS MasterMap Topography Layer. It is an enhancement to, and forms part of, OS MasterMap Topography Layer.

Building Height Attribute contains height values for buildings, tanks, chimneys (industrial) and glasshouses, specifically for Topographic Area features with the theme of ‘Buildings’ within OS MasterMap Topography Layer. It is necessary to join the Building Height Attribute data to the corresponding OS MasterMap Topography Layer feature to which it belongs, identified by the building topographic identifier (TOID). As such, an OS MasterMap Topography Layer licence is required to use the Building Height Attribute data.

The Building Height Attribute data provides full national coverage.

Index

This technical specification includes the following sections:

• Product supply

• Product structure

• Feature type

• Code list

• Example record

A code list is a controlled set of values for an attribute. This section identifies the code lists used within OS Open Rivers and describes their values.

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]

This section describes the single feature type that makes up the OS MasterMap Topography Layer – Building Height Attribute product. The Building Height Attribute feature type has 10 attributes. The following information is given about each attribute:

Attribute Name and Definition

The name of the attribute and what it is describing.

Attribute Type

The nature of the attribute. The following values may occur:

Multiplicity

Describes how many times this element is expected to be populated in the data. An attribute may be optional or mandatory within the product as denoted by the following:

• [1] indicates that the attribute is mandatory and can only occur once.

• [0..1] indicates that the attribute is optional; if present, it only occurs once.

Product supply format

Building Height Attribute data is supplied in comma-separated values (CSV) file format. Files will not be compressed.

Product supply mechanism

OS MasterMap Topography Layer – Building Height Attribute is supplied as an online download. You can download data in CSV format from the .

The product is currently still available for customers to request through .

Building Height Attribute is supplied in 5 km² geographic chunks. Each 5 km² chunk will contain Building Height Attribute values for any building polygon that intersects that area. As such, any Building Height Attribute values that fall across tile boundaries in contiguous tiles will be duplicated.

Tiles are supplied with all available data contained within them. Not all 5 km² tiles will have complete coverage.

File naming in the product

The CSV files are named as the 5km2 chunks they correspond to, for example:

• TQ2060 for TQ26SW

• TQ2065 for TQ26NW

• TQ2560 for TQ26SE

• TQ2565 for TQ26NE

OS MasterMap Topography Layer – Building Height Attribute consists of three absolute height values and two relative height values for each building polygon. The included structures – tanks, chimneys (industrial) and glasshouses – are not distinguished from the buildings in this dataset. As such, they are subject to the same attribution and parameters. The unit of measurement used for absolute and relative building heights is metres.

Absolute heights

The absolute building heights describe the height of the buildings and selected structures at three distinct points. They are measured against Ordnance Datum Newlyn (ODN) and require the use of other height products (for example, ) to give meaningful heights to the building features. If we have been unable to calculate a valid value or have insufficient confidence in a value for any of these attributes, the fields will be populated as NULL.

Relative heights

Relative building heights have been generated from the absolute height values. These provide height values that can be utilised without the use of other height products. If we have been unable to calculate a valid value or have insufficient confidence in a value for any of these attributes, the field will be populated as NULL.

Model overview for CSV

UML model of Building Height Attribute data in CSV format

The Unified Modeling Language (UML) model of OS MasterMap Topography Layer – Building Height Attribute in CSV format can be seen in the figure below:

Code list: BHA_ConfValue

List of values describing the confidence we have in the accuracy of the Building Height Attribute values per building.

Data will be supplied as a comma-separated values (CSV) file and will appear in the following format:

osgb1000000347730836,3,2017-5-14,HP6510,26.2,32,34.1,5.8,7.9,99

where:

osgb1000000347730836 (TOID)

3 (version)

2017-5-14 (process date)

HP6510 (tile reference)

26.2 (AbsHmin)

32 (AbsH2)

34.1 (AbsHMax)

5.8 (RelH2)

7.9 (RelHmax)

99 (confidence level)