This section gives an overview of the nine themes of OS MasterMap Topography Layer:
Administrative Boundaries
Buildings
Heritage and Antiquities
Land
Rail
Roads, Tracks, and Paths
Structures
Terrain and Height
Water
The main features of each theme are described in the following sub-sections. More detailed information about the nine themes, including the rules that govern which theme or themes are assigned to a feature, can be found in the product's Technical Specification.
Wherever possible, real-world objects are represented in their true surveyed position. However, for the sake of clarity of display or plotting, real-world objects may be generalised (for example, small juts in house fronts may not be shown). The normal methods of generalisation that can be applied to features are:
Emphasis
Selection for inclusion
Simplification
Omission
Real-world objects may also be simplified in the OS MasterMap Topography Layer, for example, a small group of trees may be recorded as a single point or polygon feature. The following sub-sections give a breakdown, by feature type, of the nine themes in greater detail, including regional and cultural special designations.
Administrative boundaries are defined as showing the limits of responsibility and representation for electoral and administrative purposes. Boundary alignments are shown within the Administrative Boundaries theme. As well as the boundary’s relationship to real-world objects, its mereing and boundary descriptions, where needed for clarification, are also supplied.
Buildings are defined as permanent roofed constructions, usually with walls. This includes permanent roofed constructions that exceed 8.0m² in area (12.0m² in private gardens). Exceptions are made to this area rule for smaller buildings that, due to their detached position, form relatively important topographic features; these are shown at minimum size, as stated above. With a few exceptions (for example, by describing government offices or hypermarkets), no distinction is currently made between residential, private, public, commercial, or industrial buildings.
For Ordnance Survey purposes, antiquities are defined as existing artificial features of a date not later than AD 1714 (the date of the accession of George I). These antiquities are captured along with very important battlefield sites and natural features connected with important historic events. Features and sites of a date later than AD 1714 may be treated as antiquities as an exception if they are of national importance.
The investigation, recording and surveying of archaeology is the responsibility of English Heritage, Historical Environment Scotland (HES) and Cadw (Wales). Antiquity find sites are not shown in OS MasterMap Topography Layer. Ordnance Survey has no responsibility for defining the authenticity of distinctive or descriptive names of antiquities.
A land feature is defined as either a man-made or a natural polygon feature that describes the surface cover and area to which it is applied. This includes both natural and man-made slopes and cliffs. All general features are also placed in the Land theme. There are some exceptions to this, such as routes of communication and buildings.
Rail features are defined as features related to travel by railway or tramway. The exception to this is railway tunnels, which are currently in the Structures theme. OS MasterMap Topography Layer contains information relating to permanent railways that form the network between two points, for example, from railway station to railway station, or from an industrial building to a private quarry.
For Ordnance Survey purposes, a road is defined as a metalled way for vehicles. Roads that form part of the public network and driveways to private properties that are over 100m in length are normally included within OS MasterMap Topography Layer.
A track, for Ordnance Survey purposes, is defined as an unmetalled way that is clearly marked, permanent and used by vehicles. Tracks are only normally recorded in private gardens if they are 100m or more in length. They need not be ‘all weather’. All tracks are described as ‘Track’, or ‘Tk’ if required to be abbreviated. Distinctively named tracks have their name recorded, for example, HICKS LANE (Track).
For Ordnance Survey purposes, a path is defined as any established way other than a road or track. They can be considered as either ‘made’ or ‘unmade’.
Structures are defined as features that are man-made constructions but do not qualify as buildings
(for example, Band Stands and Clock Towers). These features may or may not obstruct passage at ground level. OS MasterMap Topography Layer contains information relating to all permanent structures that are considered large enough to be included.
These are features that denote the ground level at any given point. OS MasterMap Topography Layer does not contain height contours; instead, it contains height information point features of known height.
Water features are defined as features that contain, delimit, or relate to real-world objects containing water.