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.

Physical features shown in the Buildings theme include:

• Roofed Buildings (identified as being of sufficient size or importance to be shown)

• Mobile or Park Homes that are permanent, residential and have a postal address

• Archways and Covered Passageways, where the alignment can be determined from outside the building

• Horticultural Glasshouses over 50m²

• Covered Tanks

Features such as cooling towers, uncovered tanks, bridges, and monuments are shown within the Structures theme.

Only glasshouses over 50m² that serve a horticultural purpose will continue to be captured as glass structures. Other glass structures, such as office buildings and conservatories, exist within OS MasterMap and will be recorded as buildings. There are some non-physical features shown in the Buildings theme, represented as the following text features:

• House Numbers

• Descriptive Building Names

• Distinctive Building Names

Detail in private gardens attached to residential buildings, such as sheds, pathways and ornamental ponds, is not captured as part of the specification. Where possible, all gardens of this type are generalised and represented by a single garden polygon.

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.

The following types of boundary are shown within the Administrative Boundaries theme:

Parliamentary boundaries

In Great Britain:

• County Constituency

• Borough Constituency (England and Wales)

• Burgh Constituency (Scotland)

• Assembly Electoral Region and Assembly Constituency (Wales)

• Parliamentary Electoral Region and Parliamentary Constituency (Scotland)

Local Government boundaries

In England:

• County

• City and County of London, District, London borough, Unitary Authority, and Metropolitan District

• Civil Parish and the Inner and Middle Temples

• Electoral Division

• Ward

In Wales:

• Unitary Authority

• Community

• Electoral Division

In Scotland:

• Unitary Authority

• Ward

Physical features shown in the Administrative Boundaries theme include:

• Boundary Posts

• Boundary Stones

• Boundary Markers

Non-physical features shown in the Administrative Boundaries theme include:

• Alignments of Boundaries

• Textual Descriptions of Boundaries, Mereings and Posts and Stones

Application of precedence

Where two or more boundaries are coincidental, a single alignment is shown by the most important boundary in the following order:

In England and Wales:

• County, City and County of London, Unitary Authority, District, London Borough and Metropolitan District, Civil Parish, Community, Inner and Middle Temples

• European Electoral Regions, County / Borough Constituencies

• Welsh Assembly Electoral Region

• Electoral Division and / or Ward

In Scotland:

• Unitary Authority

• European Electoral Regions, County / Burgh Constituencies

• Scottish Parliamentary Electoral Region

• Ward

A textual description often accompanies this occurrence and is used for clarification. If the alignment of an administrative boundary coincides with any other feature (other than another boundary), then both will be shown in their respective themes.

More information on administrative boundary alignments can be found here.

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.

Due to the variety of physical features in the Heritage and Antiquities theme, an exhaustive list is not provided, but the following are included:

• Standing Stones

• Earthworks

• Hill Figures

• Ruined Buildings

• Tombs

• Stone Circles

Some non-physical features are shown in the Heritage and Antiquity theme, including:

• Textual Descriptions for the real-world objects

• Battle Sites, as either text or a symbol

There are some limitations on what can be shown, imposed by survey principles. Many earthworks are of low relief and do not meet Ordnance Survey’s minimum criteria. To depict the feature clearly, it may be necessary to exaggerate antiquity detail. In mountain and moorland areas, some antiquity features may be generalised, without losing the essential characteristics of the depiction.

Roads

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.

Tracks

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).

Paths

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’.

Made paths

Made paths are those whose surface is paved or metalled. Only major paths are shown in parks, public gardens, cemeteries and so on. Made paths are described by the annotation ‘Path’, except in built-up areas, where the description will not normally be recorded. Distinctive names, such as ‘Simmons Walk’, are also included as part of OS MasterMap Topography Layer.

Unmade paths

Unmade paths are those that are neither paved nor metalled. An unmade path is included in OS MasterMap Topography Layer when its entire length is evident on the ground and it starts at a road, track or path and finishes at a similar feature or a specific place of interest. Unmade paths are described by the annotation 'Path (um)' in urban and rural areas.

Physical features shown in the Roads, Tracks and Paths theme are listed below:

Kerb lines or the limits of metalling:

• Carriageway Limits, including any hard shoulder or shallow drainage gullies forming the side of the road on dual carriageways or motorways

• Kerbed Roundabouts

• Traffic Islands in roads (usually 8m² or more)

• Traffic-calming measures forming a physical obstruction, including pinch points

• Dedicated Cycle Lanes

• Fords

• Car Parks

• Edges or centre alignments of tracks and paths

• Step treads

Road furniture:

• Mile Posts

• Guideposts (traditional fingerposts only)

• Kerb Barriers

• Gates across roads

• Posts preventing vehicular access

• Weighbridges

• Cattle Grids

Road-bounding features:

• Hedges, Walls, Fences, and Banks

• Crash Barriers (where they form the sole bounding feature of a carriageway)

Non-physical features shown in this theme are represented as distinctive and descriptive text and inferred links.

There are two situations where constraints on how the features are depicted are normally imposed by survey tolerances:

• Where the central alignment of an unmade path is less than 1m (urban areas) or 2m (rural and moorland) from an adjacent building, fence, hedge or wall, the central alignment is shown at that minimum distance away from the feature.

• Where one edge of a track is parallel and close to the bank of a water feature, the track edge nearest to the river is omitted.

It is important to note that rights of way are not identified in OS MasterMap Topography Layer. The representation of a road, track or path cannot be used as evidence of a right of way.

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.

Standard-gauge railways are shown to scale by a pair of rails and represent tracks 1.435m apart. Railways narrower than 1.435m are deemed to be narrow gauge and are shown by a single line representing the central alignment. Tramways, metros, and light-rapid-transit systems are treated as railways.

Underground portions of the Metropolitan and District lines in London that are close to surface level are shown; where a deep-level tube railway comes to the surface and continues as a normal railway, it is shown as a standard-gauge railway. In other cities, only the sections of underground railways that are open to the sky are currently shown.

Physical features shown in the Rail theme include:

• Level Crossings

• Lighting Towers

• Loading Gauges

• Turntables

• Mile or Kilometre Posts and Stones

• Sand Drags

• Signal Posts, Bridges, and Gantries

• Switches and Slips

• Retarders

• Bridges and Viaducts

• Mail Pick-ups

• Rails

• Permanent Ways

• Station Buildings and Platforms

Some physical features are not shown in the Rail theme:

• Telephones associated with Level Crossings

• Conductor Rails and Overhead wires for electrified trains

• Detail beneath the roofs of Railway Stations

• Water Troughs

• Repetitive Features, such as signal lights within marshalling yards

Some non-physical features are shown in the Rail theme: these are text descriptions of railway and associated railway features.

OS MasterMap Topography Layer is comprised of nine themes:

• Administrative Boundaries

• Buildings

• Heritage and Antiquities

• Land

• Rail

• Roads, Tracks, and Paths

• Structures

• Terrain and Height

• water

The following sub-sections describe the main features and content of each theme in detail. This will aid users’ understanding of which features they can find in the data and the most likely theme(s) that the feature will be found in. The rules governing which theme or themes are assigned to a feature are discussed in theme rules.

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, parallel features and 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 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 themes in greater detail, including regional and cultural special designations.

Theme rules

There are several rules that govern what theme or themes are assigned to a feature. These rules give the data consistency so that the same kind of real-world objects are assigned to the same themes as far as possible.

There is one attribute – called the descriptive group attribute – that has a major bearing on the theme rules. The value in the descriptive group is the key determinant of which theme(s) is / are assigned to a feature. The table below relates the value of descriptive group (of which there are 21) to the theme. If the feature has the value listed in the first column, it will be assigned into the theme listed in the second column.

There are some additional rules for assigning lines to themes. Lines serve two purposes in OS MasterMap Topography Layer. There are lines that are coincident with the boundaries of polygon features; these are called bounding lines and they are the most common type of line. However, some lines do not form boundaries to features, but are a feature in their own right; these are called non-bounding line features.

In addition to being a member of each theme rule, a line feature that is part of the boundary of one or more polygon features is also considered a member of the theme of those polygon features which it bounds. For example, any line feature that bounds a polygon feature that is a member of the Roads, Tracks and Paths theme is also a member of the Roads, Tracks and Paths theme, in addition to any other themes to which it belongs. The image below gives examples of the application of theme rules:

The product themes pages discuss the themes of OS MasterMap Topography Layer and outline the contents of each theme and explain how Ordnance Survey allocates a feature to one or more themes. This helps users to understand which theme a feature is likely to be found in, and why some features may appear in a theme that may not seem logical on first appearance.

Water features are defined as features that contain, delimit, or relate to real-world objects containing water.

Physical water features shown in OS MasterMap Topography Layer include:

• Mean High Water (springs) and Mean Low Water (springs)

• Swimming Pools, Ponds, Lakes, and Lochs

• Moats, Bridges, and Footbridges

• Reservoirs, Rivers, Canals, and Streams

• Drains and Ditches

• Foreshore Features

• Floating Objects (they are only shown when they are fixed and attached to permanent detail)

• Shake Holes and Swallow Holes (in mountain and moorland areas; limits of numerous shake holes are shown, and the area described as ‘area of shake holes’)

• Sluices (except those found in sewage works) and Culverts

• Stepping Stones

• Taps (which take the form of drinking fountains or that form the communal water supply), Drinking Fountains and Water Troughs (public)

• Tidal Gauges

• Waterfalls (only if formed by natural features) and Weirs

• Bollards, Capstans, and Mooring Posts

• Breakwaters and Groynes

• Perches, Pilot Beacons, and Navigational Beacons

• Pumps, Wells, Spouts, Springs, and Fountains

Taps, water troughs and drinking fountains are no longer captured under the current specification.

The image below shows a sample of real-world objects in the Water theme, including a pond, a river, flow arrows, sluices, and drains:

Non-physical features shown in the Water theme are:

• The highest point in a river to which normal tides flow; this is described as the Normal Tidal Limit (NTL). The point is shown and annotated with text.

• Low Water Level (LWL); this is the point to which mean tides (or mean spring tides in Scotland) flow at low water. The point is shown and annotated with text.

• Textual descriptions of all water features.

• Flow arrows, which are symbols used to indicate the direction of flow of non-tidal moving water.

As water is a dynamic element within the landscape, certain survey principles and constraints are imposed on the representation of water within OS MasterMap Topography Layer.

Rivers, streams, and drains are shown at their true scale width. A single line is normally used where their width is less than:

• 1.0m in urban areas

• 2.0m in rural, mountain and moorland areas

OS MasterMap Topography Layer does not contain polygons of the open sea. Where inland water bodies meet the sea, the following principles are applied:

• Ordnance Survey shows high and low water marks of a mean average tide, that is, an average tide halfway between spring and neap tides in England and Wales, and of average spring tides in Scotland.

• In tidal rivers, the point to which mean tides (or spring tides in Scotland) flow at high or low water is included.

Lakes and ponds are surveyed at normal winter level; reservoirs are shown at top water level, that is, spill over level. All water features are described. Continuous topographical water features that extend into private gardens are shown. Where a river flows under another object, typically a bridge, the part of the river beneath the object is not supplied. This is why there are gaps in rivers when the theme is viewed on its own. An example of such a gap in a river is shown below:

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.

Landform features, such as slopes and cliffs, behave slightly differently from other features as in the instances that they are represented as line features, they can cross other line features without being broken at the intersection of the line. Additionally, when they are polygon features, they can overlap other polygon features instead of sitting adjacent to them.

The Land theme encompasses those areas that do not form part of another theme. For example, a grass verge next to a road would appear in the Roads, Tracks, and Paths theme, whereas a grass area within a park would be in the Land theme.

The limits of geographic features such as hills and valleys are not recorded, although the distinctive names of these geographic features are shown when applicable.

Physical features shown in the Land theme include:

• Recreation areas such as Parks, Playing Fields, Football Pitches, and Golf Courses

• Slopes and Cliffs

• Car Parks

• Gardens

• Woodlands

• Areas of Vegetation (including scrub, heath, rough grass, and marshland) The Land theme also contains text features that describe the physical features.

In the image below, different types of vegetation cover have been identified on the edges of a settlement. Each type of vegetation has been labelled using the attribution within OS MasterMap Topography Layer:

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. The image below gives some examples (highlighted in dark grey) of structures:

Physical features in the Structures theme include:

• Stand-Alone Monuments

• Fountains

• Covered Reservoirs

• Pylons

• Weirs and Sluices

• Gas Holders

• Double Walls

• Pontoons

• Uncovered Tanks

• Conveyors

• Cooling Towers

• Upper Levels of Communication

• Bridges, Viaducts, Aqueducts, and Piers Non-physical features are represented by text.

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.

Triangulation stations

These are physical marks that represent points in the national triangulation scheme. The best-known form is the triangulation pillar, often found on hill or mountain tops. Other forms include triangulation points placed on church towers and flagpoles. The coordinates of a triangulation station in the data are not usually the very accurate coordinates for the control point. The accurate coordinates of the control point can be obtained from Ordnance Survey (see sub-section below on spot height). All triangulation stations are shown, except for buried and surface blocks.

Spot height

These are non-physical points, the altitude of which (relative to Ordnance Datum) has been determined by levelling. All current spot heights are shown by a point feature or symbol. The altitude to one decimal place of a metre is shown by a textual description. The latest information on Ordnance Survey’s GPS, triangulation and control points can be found on the .

Bench marks are represented in OS MasterMap Topography Layer as a symbol to mark their position. The values for these bench marks are available from the . It should be noted that the bench mark information is historic, and Ordnance Survey cannot guarantee its accuracy.