DNF Base Reference Objects Base reference objects for the Digital National Framework Digital National Framework Topographic Area Any topographic feature type represented as a polygon. descriptiveGroup theme descriptiveTerm make physicalLevel physicalPresence fid featureCode version versionDate calculatedAreaValue Topographic Line Any topographic feature type represented as a line. fid featureCode version versionDate theme accuracyOfPosition changeHistory descriptiveGroup descriptiveTerm nonBoundingLine heightAboveDatum heightAboveGroundLevel make physicalLevel physicalPresence polyline Topographic Point Any topographic feature type represented as a point. fid featureCode version versionDate theme accuracyOfPosition changeHistory descriptiveGroup descriptiveTerm heightAboveDatum heightAboveGroundLevel make physicalLevel physicalPresence point Boulders An area of large (>0.2 m dia) rounded rocks (weathered or water worn) up to 20.0 m apart. The limit to areas of boulders below MHW (S), not associated with other rock features and regardless of size of area, are captured. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Boundary post or stone A post or stone that is used to mark the extent of an administrative boundary. Any post which is reputed or recognised by local authorities to relate to a current administrative or electoral boundary is captured and described as appropriate. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Building A permanent roofed construction. Includes permanent mobile/park homes and caravans that are self contained, occupied principally for residential purposes and have postal addresses. Garages are captured when they meet the generic specification criteria. Portable, semi-portable buildings or structures such as portakabins, caravans without postal addresses, etc. are not captured with the exception of prefabricated classrooms within school grounds expected to remain for more than 10 years. A building attached to a larger building, but of completely different construction, is treated as a separate building and captured as a separate feature with the exception of such buildings within private gardens attached to private residential dwellings when they are captured as one feature. A building attached to a larger building of the same type of construction are considered part of the larger building and captured as a single feature. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Building Archway Passage or arched entrances beneath a roofed construction. These are captured when the limits can be surveyed from the outside of the building or structure, are generally more than 2m in width, and can be used by vehicles. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Building edge - Overhanging The alignment of an overhead building edge. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Building wall - External The external wall of main buildings. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Building wall - Internal The alignment of an obvious internal building division. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Coniferous trees An area of coniferous (cone-bearing) trees spaced at not more than 30 m apart. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Coppice An area of non-coniferous species of tree, which is either regularly or intermittently, cut to the ground, eg hazel, chestnut and willow (osiers). osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Culvert alignment The alignment of a large culvert portal. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Development An area of land that is in the progress of being developed. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Edge of inland water The edge or alignment of an inland water feature e.g. drain, stream, river or lake. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Edge of road or track The non-obstructing edge of a road or track. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Footbridge A raised structure for pedestrian passage across an underlying feature. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Ford A shallow part of a flowing water which may allow vehicular access. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Foreshore The area of land lying between MHW and MLW, or MHWS and MLWS in Scotland. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Glasshouse A horticultural building constructed largely of glass. Only commercial glasshouses are captured. Greenhouses in private gardens are not captured. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Heath An extensive area of open land covered with heather or bilberry with very few trees or bushes. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Historic Feature The extent of a historic feature. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Historic structure A positioned structure of historic interest. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Inland water An area of fresh water, the extent of which is captured at normal winter level. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Lattice tower A metal structure that houses or supports equipment e.g. lighting, wireless transmission, electricity transmission lines. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Level crossing A junction where a railway line crosses a road, captured by defining the limits of the crossing across railway land. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Manmade surface A manmade surface area. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Marsh An area of ground that is waterlogged throughout the year, it may include bulrushes or reeds. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Mean high water line The alignment of the mean high water tide line (spring tide limit in Scotland). osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Mean low water line The alignment of the mean low water tide line (spring tide limit in Scotland). osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Minor detail Line work that defines the edge of ancillary minor features e.g. alignments of non-obstructing such as pipelines at ground surface level. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Mixed natural An area of mineral and mixed vegetation consisting of 2 or more types. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Mixed vegetation An area of vegetation consisting of 2 or more vegetation types. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Moveable structure An area that represents the extent of a moveable structure e.g. moving greeenhouse, moveable crane. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Natural surface Areas of natural surface with no specific vegetation classification e.g. agricultural land. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Non coniferous trees Area of trees that do not bear cones, spaced at not more than 30 m apart. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Non obstructing feature Alignment of permanent detail that is not an obstruction at ground level e.g. features <0.3 m high, broken hedge, baulk, broken bank, kerb (other than public road), edge of metalling (other than public road), track, broken wall, outline of elevated features, for example, overhanging roofs less than 50 m2 and gantries. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Obstructing feature Alignment or outline of permanent detail forming an obstruction greater than 0.3 m above ground level e.g. hedge, fence, bank, wall, minor building outline. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Orchard Cultivated fruit trees, e.g. walnut, apple. Only commercial orchards are captured. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Overhead structure An overhead manmade structure. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Path A strip of ground specifically for pedestrian or bicycle use that may be a made surface or ground worn down by the passage of people on foot or bicycle. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Path alignment - Unmade The alignment of an unmade path. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Pavement A manmade area adjacent to a road. Generally for pedestrians but can include central reservations on motorways and dual-carriageways. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Private garden An area containing multiple surface types representing private residential gardens. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Property closing line Lines closing off inferred property extents. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Rail structure A point structure feature adjacent and related to rail. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Rail structure extent An area structure feature adjacent and related to rail. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway - Narrow gauge track Alignment of the track of a narrow gauge railway. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway - Standard gauge rail Alignment of the rails of a standard gauge railway. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway buffer The alignment of railway buffer features. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway building Buildings adjacent to rail track and considered as being managed as rail property. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway land - manmade A manmade surface adjacent to rail track and considered as being managed as rail property. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Railway land - natural A natural surface adjacent to rail track and considered as being managed as rail property. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Reeds A area of freshwater reeds. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Ridge or rock line The alignment of a distinctive ridge or rock line. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Road A metalled way for vehicles. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Roadside building A building adjacent and related to a road. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Roadside structure A point structure feature adjacent a road. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Roadside structure extent An area structure feature adjacent a road. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Rock An area of exposed bedrock of >25% of the area. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Rough grass Areas of bracken and uncultivated grassland, often tufted with a 'hummocky' appearance, and normally found on the higher parts of hills, mountains and downland. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scattered boulders An area of large (>0.2 m dia) rounded rocks (weathered or water worn) more than 20.0 m apart. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scattered coniferous trees An area of coniferous (cone-bearing) trees spaced at more than 30 m apart. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scattered non-coniferous trees Area of trees that do not bear cones, spaced at more than 30 m apart. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scattered rock An area of scattered exposed bedrock (<25% of area). osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scree A mass of loose stones on the steep side of a mountain (slopes of angular rock debris). osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Scrub Area of shrubs and bushes including rhododendrons, brambles, gorse and broom. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Steps A made area using a series of raised areas which links surfaces at different heights. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Steps limit The top or bottom edge of an area of steps. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Structure A point manmade structure feature e.g. letter boxes, telephone call boxes. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Structure extent The extent of a structure area feature. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Tidal road An area of road or track that is covered by the tide. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Tidal water Areas of permanent tidal water beyond the mean low water(springs) line. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Track An unmetalled way for vehicles with wheels on both sides of their body, including vehicles designed for cross country travel and agricultural tasks. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Traffic calming Physical features on the road surface, designed to slow the flow of traffic. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Traffic calming edge Representation of the limits of features on the road surface designed to slow the flow of traffic. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Triangulation point or pillar An Ordnance Survey triangulation point or pillar created to supply and maintain positional control. osgb:TopographicPoint make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Tunnel edge The alignment of a tunnel edge. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Unknown surface A surface area of unknown nature. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Upper level of communication An area representing an upper level of communication in a complex multi level building. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Vegetation limit The alignment of the extent of an area of vegetation. osgb:TopographicLine make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Verge A managed natural area adjacent to a road. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Water structure - manmade A manmade inland water structure. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence Water structure - natural A natural inland water structure. osgb:TopographicArea make descriptiveGroup descriptiveTerm physicalLevel physicalPresence The calculated area of an area feature polygon in square metres. 1 Real Number Square Metre Indicates that a TopographicLine feature is not on the boundary of a TopographicArea feature. This is either a Polyline or a Multiline geometry. In TopographicLine features this will only be a Multiline if there is a problem with the geometry that is indicated by the broken metadata flag. The unique identifier of a feature. The OS MasterMap unique identifiers are in the form "osgb<toid>" where <toid> is a number up to 16-digits in length, and "osgb" is a DNF prefix referring to Ordnance Survey Great Britain. Topographic features have a numerical feature code (a five-digit integer) assigned to each feature. This feature code is wholly determined by the feature type (see Feature type earlier in this chapter), the descriptive group(s) and the descriptive term(s). The feature code does not add any information to that contained in these attributes. The physicalLevel, physicalPresence and make attributes do not affect the feature code. The feature code itself is arbitrarily assigned, and is therefore not informative without the look-up table that gives the feature type and attribute values corresponding to each feature code. The version number of the feature (in the range 1 to 4294967295). This uniquely identifies a specific version of a feature with a given TOID. 1 Integer The date on which this version of the feature became the current version. This is the date on which the feature was changed in the database, and is not the date of any associated real-world change. 1 A theme that the feature belongs to. 1..* Character String Administrative boundaries The limits of responsibility and representation defined for electoral and administrative purposes. Buildings Roofed constructions, usually walled. This includes permanent roofed constructions that exceed 8.0 square metres in area (12.0 square metres in private gardens). Exceptions are made for smaller buildings in such a detached position that they form relatively important topographic features. Storage tanks may be classified as buildings. Heritage and antiquities Features and cartography that depict sites or constructions of historic interest. This theme is currently very limited in content. Land Man-made and natural features that delimit and describe the surface cover other than communication routes and buildings. This also includes all features relating to man-made and natural slope and cliff. All general features are also placed in the land theme. Rail Features related to travel by railway or tramway. Currently, railway tunnels are not classified as railway and so will be present in the structures theme. Roads, tracks and paths related to transport by vehicles, cycles or pedestrians. This includes features that are road, made paths or text classified as road, track or path related. All tracks and unmade paths are not currently classified as such and so will be available in the land theme. Road tunnels are not classified as related to roads and so will be present in the structures theme. Structures Man-made constructions that are not buildings. These may or may not obstruct passage at ground level. Terrain and height Terrain-related features, some of which have associated heights (spot heights). Water Features that contain, delimit or relate to real-world objects containing water. The accuracy of a horizontal position in metres at the 95% confidence level. Character String 1.0 m Urban data capture standards (1:1250 scale). This is the nominal accuracy of a point position at the 99% confidence level. 2.5 m Rural data capture standards (1:2500 scale). This is the nominal accuracy of a point position at the 99% confidence level. 6.0 m Rural overhaul data capture standards. This is the nominal accuracy of a point position at the 99% confidence level. This is the accuracy to be expected in areas of original 1:2500 scale overhaul mapping that have not been subject to positional accuracy improvement. 8.0 m Mountain and moorland data capture standards (1:10 000 scale). This is the nominal accuracy of a point position at the 99% confidence level. Unknown The expected positional accuracy is unknown. Information about the change history of a feature and comprises the reason for the change (reasonForChange attribute) and the date for this change (changeDate attribute). 1..* This contains information about the height above OND (heightAboveDatum attribute) and where known the accuracy of this value (accuracyOfHeightAboveDatum attribute). Real Number Metre This defines the height above ground level of a feature (heightAboveGroundLevel attribute) and defines the accuracy of this where known (accuracyOfHeightAboveGroundLevel attribute). Real Number Metre A pair of easting and northing ordinates in metres, defining a horizontal location in the British National Grid spatial reference system. Where known indicates whether the real world nature of the feature is man-made or natural. 0..1 Character String Manmade Features that have been constructed, for example, areas of tarmac or concrete. Multiple Features that are a mixture of makes but are not depicted separately within the data, for example, the area around a dwelling may be a mixture of made and unmade surfaces. Natural Features that are not man-made but possibly man altered, for example, cliffs, areas of water and uncultivated/cultivated vegetation. Unclassified Features that have not had a Make allocated. Unknown Features the Make of which is not known. This is the primary classification attribute of a feature. It assigns a feature to one or more of 21 groups, most of which are categories of real-world topographic objects such as path, building or natural environment; others are categories of supportive or administrative features such as network or polygon closing geometry and political or administrative. In general, values of this attribute are not specific to particular feature types. Due to limitations in the source data from which OS MasterMap was created, there are some exceptions to this principle. For instance, the descriptiveGroup buildings or structure contains text describing or naming buildings and structures, while the topographic features have the descriptiveGroup values of building, glasshouse or structures. 1..* Character String Building Features representing buildings (not including glasshouses). Buildings Or Structure Text features describing or naming buildings and structures. Built Environment Geographic areas and extents of man-made environments, terrain and communication links. General Feature General topographic features and minor detail. General Surface Features representing, describing or limiting areas of land not covered by buildings or structures. Glasshouse Features representing glasshouses. Height Control Features with height information. Historic Interest Features of heritage value. Inland Water Features representing, describing or limiting areas of water that are not tidal. Landform Features representing, describing or limiting areas of landform, for example, slopes or cliffs. Natural Environment Features representing geographic areas and extents of natural environments and terrain. Network Or Polygon Closing Geometry Features used to close polygons. Path Features representing and limiting the extent of pathways. Political Or Administrative Features representing political or electoral boundaries. Rail Features representing, describing or limiting the extents of railways. Road Or Track Features representing, describing or limiting the extents of roadways and tracks. Roadside Features representing, describing or limiting the extents of roadside detail. Structure Features representing, describing or limiting structures other than buildings or glasshouses. Terrain And Height Features giving information about the altitude at a location or changes of level of the ground surface. Tidal Water Features representing, describing or limiting areas of water that are tidal. Unclassified Topographic features that have not been given a description yet. This attribute, if present, gives further classification information about the feature. A feature may have multiple descriptiveTerm attributes, but this is little used at present. Most features have zero or one descriptiveTerm attributes. A situation where multiple descriptiveTerm attributes are used is where area features have a descriptiveGroup with the value of Natural Environment. These features can have one or more descriptiveTerm attributes specifying the natural land cover types present in the area. 0..* Character String Air Height A spot height supplied by photogrammetry Archway A covered passageway through a building or structure that vehicles can be driven through. Bench Mark Bottom Of Cliff Bottom Of Slope Boulders Boulders (Scattered) Boundary Half Mereing Boundary Post Or Stone Buffer Cliff Compound Indicates that the feature covers a geographical area and encompasses a mixture of other features. Coniferous Trees Coniferous Trees (Scattered) Coppice Or Osiers County Course Of Heritage The alignment of a heritage or antiquity feature, for example, the course of a Roman road. Culvert Direction Of Flow District Disused Feature Division Electoral Foreshore Heath Inferred Property Closing Link The feature has been inferred from the surrounding topographic features in order to divide large polygons. Land Use Change Polygon Closing Link Marsh Reeds Or Saltmarsh Mean High Water (Springs) Mean Low Water (Springs) Multi Surface Narrow Gauge Network Closing Link Nonconiferous Trees Nonconiferous Trees (Scattered) Orchard Outline Overhead Construction A structure clear of the ground to allow access beneath it, for example, electricity transmission lines, cable car cables. Parish Parliamentary Pedestrianised Street Polygon Closing Link Positioned Boulder Positioned Coniferous Tree Positioned Nonconiferous Tree Public Pylon Ridge Or Rock Line Road Name Or Classification Road Related Flow Rock Rock (Scattered) Rough Grassland Scree Scrub Site Of Heritage Slope Spot Height Standard Gauge Track Step Structure Switch Top Of Cliff Top Of Slope Track Traffic Calming Triangulation Point Or Pillar Tunnel Edge Unmade Path Alignment Upper Level Of Communication Upper level of through public communication, for example, in multilevel shopping centres. This attribute states whether the feature is underground, obscured below normal cartographic level, at normal cartographic level, or overhead. Normal cartographic level is that perceived to be the normal surface level. Where area features overlie others e.g. bridges they are at normal cartographic level and the features below them are recorded as obscured. Indicates the physical level of a feature with reference to the normal cartographic surface level. Only four values are used. -1 = Underground detail 49 = Obscured detail below the normal cartographic level 50 = Detail at the normal cartographic level 51 = Overhead detail above normal cartographic level 1 Integer -1 Underground detail 49 Obscured detail below the normal cartographic level 50 Detail at the normal cartographic level 51 Overhead detail above normal cartographic level This attribute indicates the nature of the object represented by the feature. This normal used for TopographicLine, for example, a value of obstructing indicates that the feature prevents pedestrian access, whereas a value of edge/limit means that the feature represents a change of surface type and does not generally impede access. This attribute is also used to identify admin boundary and inferred line features, and moveable area feature (e.g. moveable cranes). 0..1 Character String Boundary Indicates that the feature is a political or administrative boundary, for example, European region, county, ward, civil parish and so on. Note: The physicalPresence for a BoundaryLine will always be "Boundary". Closing Feature not physically present. This may have been surveyed or inferred to close a polygon for reasons of classification or identity. Edge / Limit The feature is a physical definition of the edge of an area but does not obstruct pedestrian access. Extent The feature identifies a geographical area with unknown or poorly defined limits. Indicator The feature is a symbolic representation of the characteristics of physical features, for example, direction of river flow or site of a heritage feature. Minor Detail The feature is subsidiary to surrounding detail. Moveable Indicates that the object can move within the extent of the feature, for example, a moveable crane. Network Feature represented is part of a transport network e.g. narrow gauge railway track. Obstructing Indicates that feature is normally more than 0.3 m high and forms an obstruction to passage on foot. Overhead This value indicates that the alignment of a feature is defined by something that is above the physical level of the feature. For example, this value is used if part of a building is on stilts. In that case, the PhysicalLevel attribute would be 50 (normal cartographic level).