Product themes

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.

Descriptive group	Theme	Real-world examples	Description
Buildings	Buildings	Factories, Houses, Public Convenience, Tank	Features representing buildings (not including glasshouses).
Buildings Or Structure	Buildings	Cartographic text intersecting buildings	Features representing the name, function, or use of a building or structure.
Built Environment	Land	Residential Land, Car Parks	Geographic areas and extents of man-made environments, terrain and communication links.
General Feature	Land	Cattle Grid, Conduit, Conveyor, Line of Posts, Lock Gate, Slipway, Sloping Masonry	General topographic features and minor detail.
General Surface	Land	Agricultural Land, Slag Heap, Slipway, Sloping Masonry, Spoil Heap, Tank	Features that denote surfaces that are man- made, though not specifically in man-made environments.
Glasshouse	Buildings	Greenhouses	Features representing glasshouses.
Height Control	Terrain and Height	Bench marks	Features with height information.
Historic Interest	Heritage and Antiquities	Site Of Heritage, such as a Battlefield	Features of heritage value, often depicted as text, indicating the site of a historic event or an actual physical historical structure, such as Hadrian’s Wall.
Inland Water	Water	Canals, Collects, Drains, Fords, Issues, Lakes, Leats, Reservoirs, Rivers, Sinks, Spreads, Springs, Static Water, Streams, Watercourses, Waterfalls	Features representing, describing or limiting areas of water that are not tidal.
Landform	Land	Caves, Mineral Workings, Slopes, Cliffs, Quarries	Features representing, describing or limiting areas of landform, for example, slopes or cliffs.
Natural Environment	Land	Marsh, Mud, Saltmarsh, Sand, Shingle, Scrub, Woodland	Features representing geographic areas and extents of natural environments and terrain.
Network or Polygon Closing Geometry	Land, and Road, Tracks and Paths	Road Junctions, Gardens	Features used to close network polygons at their termination.
Path	Roads, Tracks and Paths	Paths, Cycle Paths	Features representing and limiting the extent of pathways.
Political or Administrative	Administrative Boundary	County, District, Ward and Civil Parish boundaries and markers	Features representing political or electoral boundaries.
Rail	Roads, Tracks and Paths	Railway Land, Tracks and Signals	Features representing, describing or limiting the extents of railways.
Road or Track	Roads, Tracks and Paths	Road sections of varying surfaces, Roundabouts, Central Reservations	Features representing, describing or limiting the extents of roadways and tracks.
Roadside	Roads, Tracks and Paths	Verges, Pavements	Features representing, describing or limiting the extents of roadside detail.
Structure	Structures	Bridges, Chimneys, Groynes, Lighting Gantries, Lock Gates, Sluices, Telecommunications Masts, Weirs and Wind Turbines	Features representing, describing or limiting areas of water that are tidal.
Terrain and Height	Terrain and Height	Spot height marks	Features giving information about the altitude at a location or changes of level of the ground surface.
Tidal Water	Water	Tidelines, including Mean High Water (MHW) / Mean Low Water (MLW), Mean High Water (Springs; MHWS) / Mean Low Water (Springs; MLWS), Normal Tidal Limit (NTL) / Mean Spring Tide (MST)	Features representing, describing or limiting areas of water that are tidal
Unclassified	Land	Areas under temporary development	Features representing developing or undesignated attributes in the process of being captured.

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:

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.