> For the complete documentation index, see [llms.txt](https://docs.os.uk/os-downloads/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/feature-types/topographicline.md). # TopographicLine Feature representing topographic objects and concepts that have a line-based geometry (for example, Fence). * Spatial attribute: polyline * Data type attribute: GM\_Curve or GM\_MultiCurve ## TopographicLine attributes ### TOID or gml:id The unique topographic reference number. It consists of the letters ‘osgb’ followed by thirteen or sixteen digits. The TOID must always be retained/stored in its entirety and any leading zeros on the TOID are retained to permit linking of the feature to other OS MasterMap products. * **Attribute Name:** TOID or gml:id * **Type:** String * **Multiplicity:** \[1] ### featureCode 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, 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. * **Attribute Name:** featureCode (GML), feature\_code (GeoPackage), N/A (Vector Tiles) * **Type:** Integer * **Multiplicity:** \[1] ### version 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. * **Attribute Name:** version (GML), version (GeoPackage), N/A (Vector Tiles) * **Type:** Integer * **Multiplicity:** \[0..1] ### versionDate 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. * **Attribute Name:** versionDate (GML), version\_date (GeoPackage), N/A (Vector Tiles) * **Type:** Date * **Multiplicity:** \[1] ### theme A theme that the feature belongs to. * **Attribute Name:** theme (GML), theme (GeoPackage), N/A (Vector Tiles) * **Type:** [ThemeValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/themevalue.md) * **Multiplicity:** \[1..\*] ### accuracyOfPosition The accuracy of a horizontal position in metres at the 95% confidence level. * **Attribute Name:** accuracyOfPosition (GML), accuracy\_of\_position (GeoPackage), N/A (Vector Tiles) * **Type:** [AccuracyOfPositionValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/accuracyofpositionvalue.md) * **Multiplicity:** \[1] ### changeHistory Information about the change history of a feature that comprises the reason for the change and the date for this change. Each feature may have numerous change history records, and these are ordered chronologically. A complex attribute. * **Attribute Name:** changeHistory * **Type:** [ChangeHistoryType](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/complex-attributes/changehistorytype.md) * **Multiplicity:** \[1..\*] ### descriptiveGroup 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. * **Attribute Name:** descriptiveGroup (GML), descriptive\_group (GeoPackage), N/A (Vector Tiles) * **Type:** String; see [DescriptiveGroupValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/descriptivegroupvalue.md) * **Multiplicity:** \[1..\*] ### descriptiveTerm This attribute, if present, gives further classification information about the feature. A feature may have multiple descriptiveTerm attributes. Most features have zero or one descriptiveTerm attributes. A situation where multiple descriptiveTerm attributes are used is where line features have a descriptiveGroup with the value of ‘Tidal Water’. These features may have multiple descriptiveTerm attributes, for example, where Mean High Water (Springs) and Mean Low Water (Springs) are co-incident. * **Attribute Name:** descriptiveTerm (GML), descriptive\_term (GeoPackage), N/A (Vector Tiles) * **Type:** String; see [DescriptiveTermValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/descriptivetermvalue.md) * **Multiplicity:** \[0..\*] ### nonBoundingLine Indicates that a TopographicLine feature is not on the boundary of a TopographicArea feature. * **Attribute Name:** nonBoundingLine (GML), non\_bounding\_line (GeoPackage), N/A (Vector Tiles) * **Type:** Boolean * **Multiplicity:** \[0..1] ### heightAboveDatum A complex attribute that is comprised of two simple attributes. The height of the feature above the Ordnance Datum Newlyn (ODN) vertical datum (in metres) is defined in the ‘heightAboveDatum’ attribute. The accuracy of the vertical position in metres at the 95% confidence level is defined by the ‘accuracyOfHeightAboveDatum’ attribute. * **Attribute Name:** heightAboveDatum (GML), height\_above\_datum (GeoPackage), N/A (Vector Tiles) * **Type:** [HeightAboveDatumType](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/complex-attributes/heightabovedatumtype.md) * **Multiplicity:** \[0..1] ### heightAboveGroundLevel A complex attribute that is comprised of two simple attributes. The height of the feature above ground level (in metres) is defined in the ‘heightAboveGroundLevel’ attribute. The accuracy of the vertical position in metres at the 95% confidence level is defined by the ‘accuracyOfHeightAboveGroundLevel’ attribute. * **Attribute Name:** heightAboveGroundLevel (GML), height\_above\_ground\_level (GeoPackage), N/A (Vector Tiles) * **Type:** [HeightAboveGroundLevelType](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/complex-attributes/heightabovegroundleveltype.md) * **Multiplicity:** \[0..1] ### make Where known, indicates whether the real-world nature of the feature is man-made or natural. * **Attribute Name:** make (GML), make (GeoPackage), make (Vector Tiles) * **Type:** [MakeValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/makevalue.md) * **Multiplicity:** \[0..1] ### physicalLevel 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 an area feature overlies another (for example, 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 * **Attribute Name:** physicalLevel (GML), physical\_level (GeoPackage), N/A (Vector Tiles) * **Type:** Integer * **Multiplicity:** \[1] ### physicalPresence This attribute indicates the nature of the object represented by the feature. This is normally 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 administrative boundary and inferred line features, and moveable area features (for example, moveable cranes). * **Attribute Name:** physicalPresence (GML), physical\_presence (GeoPackage), N/A (Vector Tiles) * **Type:** [PhysicalPresenceValue](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-technical-specification/enumerations/physicalpresencevalue.md) * **Multiplicity:** \[0..1] ### polyline 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. * **Attribute Name:** polyline * **Type:** GM\_MultiCurve * **Multiplicity:** \[1] --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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