OS MasterMap Topography Layer Technical Specification

This technical specification provides detailed technical information about OS MasterMap Topography Layer. It is targeted at technical users and software developers.

OS MasterMap Topography Layer provides the most detailed and accurate large-scale representation of Great Britain available from Ordnance Survey. It contains features that represent objects in the physical environment, such as buildings, fields, fences, and letter boxes. It also includes intangible objects, such as county boundaries and the lines of mean high or low waters. There are over 500 million features in the product. Coverage includes the whole of Great Britain (i.e. England, Scotland, and Wales).

Key concepts

The three key concepts underlying OS MasterMap Topography Layer are:

• A feature model with identifiable and persistent features.

• Feature lifecycles defined to match actual change.

• Integration of the OS MasterMap suite of products.

Feature model

OS MasterMap Topography Layer is created on the premise of a feature-based model. This models the real world at the level of the feature, which represents an object in the real world. Each feature has an identity, location and other additional attribution.

Feature lifecycle

The features that comprise OS MasterMap Topography Layer are managed by feature lifecycle rules. These rules manage how changes in real-world objects are represented by the features in OS MasterMap Topography Layer. The rules define what real-world change constitutes a modification to an existing feature, and what change is represented by a new feature. This management allows a consistent representation of changes in the real world, based upon the capture specification.

Integration of the OS MasterMap layers

The suite of layers that make up OS MasterMap have been modelled to allow simple integration with each other. All the layers are managed in a single capture and maintenance environment, meaning the geometries of the different layers are in sympathy with each other, allowing easy integration. Additionally, they all invoke the principle of the Topographic Object Identifier (TOID) and use this as their unique IDs.

OS MasterMap layers include the following products: OS MasterMap Topography Layer, OS MasterMap Sites Layer, OS MasterMap Building Height Attribute, OS MasterMap Greenspace Layer, OS MasterMap Highways Network – Roads, OS MasterMap Highways Network – Routing and Asset Management Information (RAMI), OS MasterMap Highways Network – Paths, and OS MasterMap Water Network Layer.

Available formats

OS MasterMap Topography Layer is available the following formats:

• GeoPackage (area of interest – AOI – only)

• Vector tiles (MBTiles)

• Geography Markup Language (GML) 2.1.2

Adherence to standards

UML diagram and table conventions

The data structure in this document is described by means of Unified Modeling Language (UML) class diagrams and accompanying tables containing text.

The following colour conventions have been used in the UML diagrams and tables: feature types from the Ordnance Survey product specification are orange, data types are in purple, and enumerations are green.

Descriptive group	Feature type	Descriptive term	Feature code
Unclassified	Symbol	N/A	10214
Unclassified	Text	N/A	10213

Metadata

ISO 19115 compliant UK GEMINI discovery level metadata is provided for the data and can be found in the OS Data Catalogue.

Index

• File naming

• Supply mechanisms

• Product themes

• Feature types

• Complex attributes

• Enumerations

• Geometric data types

• Topology

• Seamless data supply

• Feature lifecycles and tracking changes

• GML overview

• GeoPackage overview

• Vector Tiles overview

• Attribute mapping

• Geometry mapping

• COU overview

• Feature code lookup table

• Change value descriptions

• Administrative boundary alignments