OS Terrain 50 | Data Products | OSOrdnance SurveyLoading...
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OS Terrain 50 is available as:
A 50m grid in ASCII grid and GML 3.2.1 (Simple Features Profile – level 0).
10m contours in Esri shapefile, GML 3.2.1 (Simple Features Profile – level 0), GeoPackage and vector tiles (MBTiles).
OS Terrain 50 is supplied as an online download, which is available with no registration required. Data can be downloaded in various formats from the Ordnance Survey Data Hub.
For the ASCII, GML and Esri shapefile formats, the data is provided as a full set of Great Britain in tiles. The national dataset is supplied as 10km-by-10km tiles of data. There are 2,858 tiles in the product which are arranged into 55 folders, with each folder representing a 100km tile grid square.
The GeoPackage and vector tile data formats are provided as a single national set within one flat file.
The product will be supplied separately for grid or contour as compressed folders for each geographic tile of data. Each compressed folder will contain data plus several additional files.
It is recommended that a download manager is used to extract the tiled data as this additional functionality will automate the process and organise the data folders as desired. There are many commercial and open-source download clients available to help manage the data.
This data is designed to be kept up to date by annual full tile resupply.
OS Terrain 50 gives full national coverage of Great Britain. The data is derived from the same source data as our large-scale revision programme that updates OS MasterMap Topography Layer.
Data will be compressed using the zip compression method and is not encrypted. Compression rates vary for contour tiles and depend upon the number of features in the geographic location.
A full national supply of OS Terrain 50 grid tiles is 157 Mb compressed.
OS Terrain 50 is supplied to customers annually each July, incorporating any updates made by the revision programme.
The source DTM for the two OS Terrain products is captured as a triangulated irregular network (TIN) by editing with mass points and breaklines and/or automated techniques within a photogrammetric environment. The TIN is a superior model for three-dimensional data as it uses triangles which can retain the edges of features more accurately than a grid.
The source data capture is subject to demanding rules defined by the height capture specification. Particular attention is paid to communication routes and features significant to height applications. This section describes some of the key capture requirements from the detailed capture specification which we endeavour to achieve in the source data.
The grid and contour forms of the products are both interpolated from this source TIN model. This is because the TIN model is not widely supported by GIS software. As OS Terrain 50 is designed to work with small-scale products, the feature modelling will have a more generalised representation in the product.
The minimum coverage of the data extends out to the low water mark, defined by Hydrographic Office tables with a height value for each tile. For England and Wales, the low water mark is Mean Low Water (MLW); for Scotland, it is Mean Low Water (Springs) (MLW(S)).
All land wholly within inland water bodies that is represented by topographic area features is captured according to the positional accuracy requirements of the area. The minimum requirement is to capture the outer edge of the feature. The surrounding water will remain flat.
Any other land within inland water bodies captured by automated processes will be removed from the data.
The z values of the source TIN data must meet positional accuracy requirements according to their geographic location. The terrain has been divided into the following three classifications to ensure that modelling reflects customer requirements:
Urban and major communication routes
Rural
Mountain and moorland
The accuracy of the height value above Newlyn Datum must achieve the root mean square error (RMSE) set for each area.
The height of the bare earth surface is recorded as a series of points with three-dimensional coordinates. The X and Y coordinates are Eastings and Northings in OSGB36; the Z coordinate is height in metres relative to the datum for the area. Most areas will record a height relative to Ordnance Survey Newlyn Datum. For a small number of offshore islands, a local datum has been used.
The bare earth surface excludes buildings, supported structures and vegetation. Structures that form an obstruction at ground level – such as dams, breakwaters and groynes (wide enough to affect the positional accuracy requirements), bridge revetments and earthworks – are considered to be part of the bare earth surface. Only permanent terrain features (those expected to remain until the next revision period or longer) are modelled.
Underground and overhead features are, by definition, not the ground surface and are thus not included in a DTM. Underground features are those that are obscured and require excavation to construct.
Underground features are not recorded, and overhead features are removed from the data.
The DTM will be free of spikes and wells that do not reflect the real-world terrain. A surface that is smooth is one that consists of a regular plane (which may be angled). For example, a road carriageway or railway track bed will appear smooth in the data.
Most data will present without visible tile edges or discernible height differences between tiles. In places, there may be small edges present or a difference in feature modelling between new and older content. There will also be small tile edges in tidal areas due to local tidal differences.
Supported structures include bridges, viaducts, cranes, elevated buildings, and jetties or piers on legs. All supported structures will be removed from the data where the structure departs from the bare earth surface and an air gap exists.
Areas of vegetation, such as hedgerows and trees, are removed to ensure that the bare earth surface is correctly recorded.
Locations with a vertical change in height or an overhang have the height of the top of the feature recorded at the correct planimetric location according to the positional accuracy requirements.
The height at the lowest point of the vertical feature is recorded according to the positional accuracy requirements of the feature but is offset from its real-world planimetric position to ensure that there is only one z value present in the same location.
Major communication routes are major road and rail networks identified in our core database.
The limits of a road carriageway or railway track bed are modelled to ensure that the route reflects its real-world shape. Modelling is required for changes in height to meet the positional accuracy requirements, to smooth the surface and to remove extraneous features, such as road furniture and bridges. Any associated slopes and embankments along the length of the route are also modelled.
In all other cases, the surface will be smooth, flat (not necessarily horizontal) and free from undulations.
The outer limits, shape and depth of mineral extraction and landfill sites are captured to meet positional accuracy requirements. Temporary features that do not represent the terrain at the time of capture (for example, spoil heaps) are removed from the data.
In order to respond to the Flood and Water Management Act 2010, the extent of all flat-water bodies that are greater than 0.7ha in area (that is, greater than 7000 cubic metres capacity) must have their limits captured to ensure that the presence of the water body can be inferred from the data. The height of the water recorded is that at the lowest height of the surrounding data. The surface of the water will be flat.
OS Terrain 50 is an open height dataset of contours with spot heights, breaklines, coastline, lakes, ridges and formlines for Great Britain. Both OS Terrain 5 and OS Terrain 50, provide detailed three-dimensional digital terrain models (DTMs) of Great Britain. A DTM primarily defines the ground surface, having removed all protruding features (such as buildings and trees) elevated above the bare earth.
This product is updated annually
OS Terrain 50 is published as both grid data and contour data in a variety of formats. Both data types are created from the same source data and are supplied as 10km-by-10km tiles. These tiles are identified by quoting the National Grid reference of the south-west corner of the area they cover.
OS Terrain 50 grid: A grid of heighted points with regular 50m post spacing.
OS Terrain 50 contours: A contour dataset of 10m interval standard contour polylines. This includes mean high water and mean low water boundaries and spot heights.
Make better decisions about where to locate wind turbines and mobile phone masts. OS Terrain 50 lets you model wind direction and lines of sight at an early stage of planning and development, meaning fewer site visits.
Get the bigger picture about flood risk, soil erosion and pollution. By showing steep hillside gradients, OS Terrain 50 helps you plan flood defences and safeguard the landscape.
With the contours version of OS Terrain 50, you can shade in hills to show their height. This extra sense of depth is ideal for walking maps and apps.
Get an accurate, uncluttered view of the terrain with the grid version of OS Terrain 50. Its 50 metre post spacing gives you a surface model of the entire landscape, including major roads, large lakes and estuaries.
The contours dataset also includes mean high and low water boundaries.
OS Terrain 50 can be used in conjunction with various Ordnance Survey digital products for analytical, modelling, planning and visual purposes.
These uses enable customers to undertake the following:
Asset/site management
Signal propagation
Environmental analysis
High-level development
Geological analysis
Line of sight planning
View shed modelling
Using the product as a visual aid
Access: Download
Data theme: Height
Data structure: Vector - DTM grid, Contour lines
Coverage: Great Britain
Scale: 1:50 000
Format: GML 3.2 Simple Features, ASCII (DTM grid), ESRI Shapefile, Vector Tiles, GeoPackage
Ordering area: All of Great Britain
Publication months: July
OS Data Hub plan: OS OpenData Plan (FREE), Public Sector Plan, Premium Plan, Energy & Infrastructure Plan
Access to this product is free through the OS Data Hub.
This section describes the structure of the data in grid and contour forms.
The height data is presented as a raster dataset of height values which are calculated at the centre of the pixel. This method of creating the data means that there are no overlaps between tiles nor common values along the edge. Coordinate reference systems for DTMs may be used to calculate the DTM origin and coordinates of individual posts.
Due to local tidal conditions, the height of the mean high and low water mark varies continuously around the coast of Britain. The mean high and low water lines have been derived from our large-scale mapping and assigned constant height values, based on the average for each tile. This average value has been determined from local tide tables. The mean high and low water lines were used as heighted breaklines when creating the grid to ensure that the grid product is consistent with the contour product. This means that there may be a small discrete step in the height of tidal water between adjacent tiles. For areas of permanent tidal water, in the grid, the height of the mean low water has been extended out to the tile edge to ensure that the tile is complete. Heights in the foreshore area are interpolated between the mean high and low water heights.
The contours are presented as polyline and spot height features. The contour lines have been divided into tiles for product supply. The contour values can be viewed and analysed in a GIS.
The terms used for the feature types are drawn from the INSPIRE elevation specification. The draft INSPIRE elevation specification requires height values to be held in an attribute called propertyValue, which has been implemented in the new OS Terrain contour GML. In the shapefile format, the GML feature types and attributes have been followed but with a 10-character limit imposed on shapefile field names, for example, propertyValue is abbreviated to PROP_VALUE.
The contours are named master and ordinary, which are equivalent to index and standard contours in Ordnance Survey’s now withdrawn product, Land-Form PROFILE.
In the contour products, the mean high and mean low water lines have been derived from our large-scale mapping and assigned constant height values, based on the average for each tile. This average value has been determined from local tide tables. Inevitably, this means that there is a small discrete step between adjacent tiles. There are no contours supplied between the mean high and low water lines.
The LandWaterBoundary feature type has an attribute of waterLevelCategory, which has four possible sub-values: meanHighWater and meanLowWater, or meanHighWaterSprings and meanLowWaterSprings for Scotland. This attribution allows their display parameters to be changed to show individual features, as desired.
Spot heights have been created using an algorithm that selects the highest source data point within every enclosed contour. As they are from an interpolated surface of the real world, they cannot be guaranteed as summits or highest points of the feature, but it is intended that, in time, the height source data will be enriched by additional spot height data. The GML data model (available in the OS Terrain 50 Technical Specification) lists the spot height sub-value of spotHeightType, which allows the potential for formSpot, generic, mountainPass or summit to be used in future releases of the product. Currently, all spot height features are attributed as generic.
It is possible that there will be some instances of spot heights recording lower height values than the enclosing contour, but it is likely that these are the result of genuine depressions.
This product may be used on a wide range of hardware platforms (provided sufficient memory and storage facilities are available), varying from tablets or computers using GIS or CAD to mainframe computers with specialised translators and applications. Please see Coverage and file size data on the product supply page for more information. Your system supplier will be able to advise on your requirements.
OS Terrain 50 is supplied as inert data in a variety of formats and does not include software for data manipulation.
GML is an open standard format, and the data may need to be translated into the appropriate format for use within a GIS application. A wide range of GIS software can read the GML contour data without translation.
The purpose of this technical specification is to:
Provide users with a brief description of the presentation of OS Terrain 50 in its supply formats.
Provide licensed system suppliers with as much detail as necessary to enable OS Terrain 50 files to be easily understood and processed by application software.
OS Terrain is the name given to Ordnance Survey’s height products. The two products available, OS Terrain 5 and OS Terrain 50, provide detailed three-dimensional digital terrain models (DTMs) of Great Britain. A DTM primarily defines the ground surface, having removed all protruding features (such as buildings and trees) elevated above the bare earth. The main difference between the two products is their level of resolution:
OS Terrain 5 is a mid-resolution DTM, designed to be interoperable with our large-scale data.
OS Terrain 50 is a lower-resolution DTM product, designed for landscape visualisation and analysis over large areas. It is an Open Data product and, as such, it is free to view, download and use for commercial, educational and personal purposes.
OS Terrain 50 is published as both grid data and contour data in a variety of formats. Both data types are created from the same source data and are supplied as 10km-by-10km tiles. These tiles are identified by quoting the National Grid reference of the south-west corner of the area they cover.
OS Terrain 50 grid: A grid of heighted points with regular 50m post spacing.
OS Terrain 50 contours: A contour dataset of 10m interval standard contour polylines. This includes mean high water and mean low water boundaries and spot heights.
OS Terrain 50 is available to download in the following formats:
A 50m grid in ASCII (American Standard Code for Information Interchange) grid and Geography Markup Language (GML) 3.2.1 (simple features profile – level 0)
10m contours in GML 3.2.1 (simple features profile – level 0)
10m contours in Esri shapefile
10m contours in GeoPackage
10m contours in vector tiles (MBTiles)
The product will be supplied separately for grid or contour as compressed folders for each geographic tile of data. Each compressed folder will contain data plus several additional files.
ASCII grid is a generic, text-based DTM format, which is sometimes referred to as ArcInfo ASCII grid or ArcGrid ASCII. This data can be read by most standard GIS software without additional translation.
Grid data is available to download in ASCII format. ASCII grid data is provided alongside GML data in the OS Terrain 50 data supply. In the gridded data supply, the .gml file effectively provides metadata (such as location, grid spacing and the vertical reference system) to allow ASCII data to be read as GML. It also contains spatial reference information in a software independent form.
The ASCII data is specified as a raster grid, with each height value being calculated from the centre of each pixel. To represent this in ASCII grid format, the initial coordinates in the map header originate on the north-west corner of the tile. The data is presented in rows that read from west to east, with 200 pixels per row. Each pixel is 50m by 50m, so the next row will begin 50m south of the origin and progress at 50m intervals to the east.
The height values are presented in the standard ASCII grid format as a series of real values. The height values are given to the nearest 0.1m.
The structure of the layers provided with the ASCII grid and GML download is outlined in the following table.
The following is the data header found in the first six rows of the ASCII grid file:
Esri shapefiles are a simple, non-topological format for storing the geometric location and attribute information of geographic features. A shapefile is one of the spatial data formats that you can work with in ArcGIS.
The shapefile format defines the geometry and attributes of geographically referenced features in as many as five files with specific file extensions that should be stored in the same project workspace. The file extensions are as follows:
.shp: The file that stores the feature geometry.
.shx: The file that stores the index of the feature geometry.
.dbf: The dBASE file that stores the attribute information of features. When a shapefile is added as a theme to a view, this file is displayed as a feature table.
.sbn and .sbx: The files that store the spatial index of the features. These two files will only exist if you perform theme-on-theme selection, spatial joins or create an index on a theme's SHAPE field.
.prj: The file that stores the projection information.
The layer structure of the Esri shapefile layers in the OS Terrain 50 contour supply is outlined in the following table.
| Layer name | Layer description |
|---|---|
OS Terrain 50 contour layers are supplied in GML 3.2.1. It is recommended that you read this section in conjunction with the Open Geospatial Consortium (OGC) document, Geography Markup Language 3.2.1. An understanding of XML (Extensible Markup Language) and XML schemas is required. The XML specifications that GML is based on are available from the World Wide Web Consortium (W3C) website.
The layer structure of the GML contour layers in the product is outlined in the following table.
| Layer name | Layer description |
|---|---|
These have been created by an automated process to select the highest mass point within every closed contour. If the point is the same height as the contour, it will be removed. It is possible that some spot heights could be lower than the surrounding contour due to genuine depressions. The z value is rounded to 0 decimal places.
The model is ‘feature-based’ so that ContourLine, SpotHeight and LandWaterBoundary are feature types with specific attributes.
The feature types within the contours are represented as individual features to enable easier interpretation. For example, the contours can be drawn as different colours to highlight the index contours, the high- water mark, and spot heights over a certain value.
The column names have been reformatted to comply with Esri software.
| Column name | Type | Description |
|---|---|---|
The ContourLine sub-type value names align with INSPIRE draft elevation specification. The terms 'master' and 'ordinary' represent the more traditionally recognised terms of 'index' and 'standard' (contours), respectively.
| Column name | Type | Description |
|---|---|---|
At launch, only the sub-type value 'generic' has been used, but the other values provide functionality to enrich the attribution if required in a later product release.
| Column name | Type | Description |
|---|---|---|
Mean High and Low Waters apply to tidal waters in England and Wales, whereas the Mean High and Low Water Springs apply to those in Scotland.
GML 3.2.1 requires features and their geometries to have unique identifiers. For OS Terrain products, the feature identifiers have been structured as follows: os.t50.<tile name>.<sequential number>, where the second part abbreviates the product name, i.e. t50 for OS Terrain 50 and t5 for OS Terrain 5. Geometry identifiers in the GML use the same form, but with a .geom suffix.
Therefore, for a given release of the product, every feature and geometry is guaranteed to have a unique identifier. The OS Terrain products will both be updated by whole tile refresh, and there are no plans to supply feature-based change-only updates (COUs). When a tile is updated, the sequential identifiers are re-generated.
The coordinate reference system for geometries in the OS Terrain 50 GML is expressed using an
EPSG code embedded in a URN (urn:ogc:def:crs:EPSG::27700). This is a more generic way of expressing the reference system, rather than osgb:BNG (British National Grid) which was used in previous versions of the product.
This product is available to try out online using one of our three sets of sample data (Exeter, Newport and Inverness) through the OS MasterMap product viewer:
| Glossary term | Definition |
|---|
OS Terrain is the name given to Ordnance Survey’s height products. The two products available, OS Terrain 5 and OS Terrain 50, provide detailed three-dimensional digital terrain models (DTMs) of Great Britain. A DTM primarily defines the ground surface, having removed all protruding features (such as buildings and trees) elevated above the bare earth. The main difference between the two products is their level of resolution:
OS Terrain 5 is a mid-resolution DTM, designed to be interoperable with our large-scale data.
OS Terrain 50 is a lower-resolution DTM product, designed for landscape visualisation and analysis over large areas. It is an Open Data product and, as such, it is free to view, download and use for commercial, educational and personal purposes.
OS Terrain 50 is published as both grid data and contour data in a variety of formats. Both data types are created from the same source data and are supplied as 10km-by-10km tiles. These tiles are identified by quoting the National Grid reference of the south-west corner of the area they cover.
OS Terrain 50 grid: A grid of heighted points with regular 50m post spacing.
OS Terrain 50 contours: A contour dataset of 10m interval standard contour polylines. This includes mean high water and mean low water boundaries and spot heights.
The product is maintained by our integrated 3 to 5-year flying programme and is synchronised with our other product updates.
There is specific modelling of significant features, particularly networks.
DTM grid data is available in ASCII (American Standard Code for Information Interchange) grid and Geography Markup Language (GML) 3.2.1, using Open Geospatial Consortium (OGC) Simple Features Profile (level 0).
DTM contour data is available in GML 3.2.1, Esri shapefile, GeoPackage and vector tiles (MBTiles).
There is full coverage of Great Britain.
It is provided free at the point of use as a download through the .
It is designed to work with Ordnance Survey’s small-scale data.
The product is updated annually in July.
It is based on the INSPIRE elevation specification.
OS Terrain 50 provides an ideal base to enable the third dimension for other data within an appropriate geographical information system (GIS). The height data has been created from a source that is also used to update our large-scale data products.
OS Terrain 50 can be used in conjunction with various Ordnance Survey digital products for analytical, modelling, planning and visual purposes. These uses enable customers to undertake the following:
Asset/site management
Signal propagation
Environmental analysis
High-level development
Geological analysis
Line of sight planning
Viewshed modelling
Using the product as a visual aid
OS Terrain 50 has been compared with GPS points in a range of sample areas to provide a route mean square error (RMSE) value for the height points in each geographic area: urban and major communication routes, rural, and mountain and moorland. OS Terrain 50 grid data has been verified to be 4m RMSE.
OS Terrain 50 is designed to be INSPIRE (Infrastructure for Spatial Data in Europe) ready. Ordnance Survey is a leading member of the UK Location Programme, which is charged with delivering INSPIRE, a directive that applies to all member states and aims to enable more joined-up data across public bodies for environmental applications.
At the time of OS Terrain's product development, the INSPIRE elevation specification had not been finalised. The data structures of OS Terrain products and the details of the GML encoding have been based on the draft INSPIRE specification.
OS Terrain 50 contours are supplied as a national GeoPackage file. GeoPackage (.gpkg) is an open, standards-based data format as defined by the OGC. It is designed to be a lightweight format that can contain large amounts of varied and complex data in a single, easy to distribute, and ready to use file.
GeoPackage can be used in most GIS software in its native format without translation. GeoPackage attribute names are not limited in length. The file size limit is very large at 140 TB*, so lots of data can be easily accommodated. GeoPackage supports raster, vector, and database formats, making it a highly versatile solution.
* A file size limit might be imposed by the file system to which the file is written.
The names of the GeoPackage layers in the OS Terrain 50 contour supply are outlined in the following table.
| Layer name |
|---|
The naming of attributes has been updated in accordance with guidelines to make them more user friendly.
| 2022 GPK Attribute name | 2023 GPK Attribute name |
|---|
The XML metadata for OS Terrain 50 follows the GEMINI metadata standard, which Ordnance Survey has committed to for the UK Location Programme and INSPIRE. Ordnance Survey has provided . OS Terrain 5 and
OS Terrain 50 also have metadata in this form, on a per-tile basis.
The XML metadata contains comments to clarify the meaning of the XML tags used in the file.
| Name | Description | Examples |
|---|
| Name | Description | Examples |
|---|
The following box displays a section of the XML file in its native format, with the location of the style sheet highlighted. It can be read like this when opened in an XML viewer or basic file reader.
The following box gives an example of how the same XML file displayed in the preceding box will look when it has been converted to HTML by the XSLT viewing style sheet.
OS Terrain Tile Metadata Product identification:
Spatial representation: grid
Tile reference: NT23NE
Topic category: elevation Coordinate reference systems: British National Grid
The XML file contains min, max, mean and standard deviation height values for the product, in a format defined by Esri. The same values are supplied for every tile. Providing these height statistics is intended to allow colour ramps to be applied by the user, such that adjacent tiles are styled consistently.
This functionality can be disabled by removing the asc.aux.xml file from each downloaded folder or adjusting the parameters of the minimum and maximum heights in a GIS, if desired.
OS Terrain 50 contour layers are supplied as a national vector tiles set in a single MBTiles file. This is a lightweight set of tiles that are efficient and fast to render in your software, provide high-resolution data, and which give a seamless experience when zooming in and out. The data is supplied in Web Mercator projection (ESPG:3857).
The vector tiles schema is detailed in the following table. In the Zoom levels columns within the table, the letter N indicates that the specified layer and attribute are not mapped within that zoom level, whereas the letter Y indicates that the specified layer and attribute are mapped within that zoom level.
| Attribute | Zoom level: 0 to 8 | 9 | 10 | 11 | 12 | 13 | 14 |
|---|
| Attribute | Zoom level: 0 to 8 | 9 | 10 | 11 | 12 | 13 | 14 |
|---|
| Attribute | Zoom level: 0 to 8 | 9 | 10 | 11 | 12 | 13 | 14 |
|---|
| Layer name | Layer description |
|---|---|
For more information about INSPIRE and UK Location, please view the .
An XSLT viewing style sheet is provided (OSTerrainMetadataViewingStylesheet.xsl) to make the xml easier to read. This style sheet converts the XML to HTML for ease of viewing in a web browser. Some browsers and other software will read this automatically if the user is connected to the internet as its address is referenced in the metadata, but you can also .
Product name:
<tile name>.asc
Esri ASCII grid data.
<tile name>.gml
Open Geospatial Consortium (OGC) file for the ASCII grid to enable the data to be loaded as GML format.
<tile name>.prj
File containing the spatial reference system in a format defined by Esri.
<tile name>.asc.aux.xml
A file which provides parameters to enable default styling in Esri applications. This ensures that the shading is consistent across the data but allows you to apply your own choice of colour ramp.
Metadata_<tile name>.xml
A metadata file for grid data, providing information on the flying date and so on.
+geometry
GM_LineString
The structure of the feature
+propertyValue
Distance
The length of the contour
+contourLineType
String
master ordinary
auxiliary
+geometry
GM_Point
The structure of the feature
+propertyValue
Distance
The z value (height above Newlyn, or other British height datum) of the feature
+spotHeightType
String
formSpot generic mountainPass
summit
+geometry
GM_LineString
The structure of the feature
+propertyValue
Distance
The length of the boundary line
+waterLevelCategory
String
meanHighWater meanLowWater meanHighWaterSprings
meanLowWaterSprings
accuracy | The closeness of the results of observations, computations or estimates to the true values or the values accepted as being true. Accuracy relates to the exactness of the result and is the exactness of the operation by which the result is obtained. |
American Standard Code for Information Interchange (ASCII) | A 7-bit code for encoding a standard character set. |
area | A spatial extent defined by circumscribing lines that form a closed perimeter that does not intersect itself. |
attribute | An attribute is a property of an entity, usually used to refer to a non-spatial qualification of a spatially referenced entity. For example, a name or descriptive code indicating what an entity represents or how it should be portrayed. |
attribute code | An alphanumeric identifier for an attribute type. |
boundary | Boundaries define the areas of the various national and local government authorities and some European authorities. |
chain | A closed loop of links bounding a polygon. |
code | An alphanumeric attribute code used in digital map data to describe each feature in terms either of the object surveyed or its representation on the map (or both). |
coding | Allocation of a feature code to a feature being created from constituent construction data – points and/or segments; with optional linking to an existing feature of the same feature code. |
contour | A line connecting points of equal elevation. |
coordinate pair | A coordinate pair is an easting and a northing. |
coordinates | Pairs of numbers expressing horizontal distances along original axes. Alternatively, triplets of numbers measuring horizontal and vertical distances. Row and column numbers of pixels from raw imagery are not considered coordinates for the purpose of the standard. |
data format | A specification that defines the order in which data is stored or a description of the way data is held in a file or record. |
data model | An abstraction of the real world that incorporates only those properties thought to be relevant to the application or applications at hand. The data model would normally define specific groups of entities and their attributes, and the relationship between these entities. A data model is independent of a computer system and its associated data structures. A map is one example of an analogue data model. |
data structure | The defined logical arrangement of data as used by a system for data management; a representation of a data model in computer form. |
eastings | See rectangular coordinates. |
entity | Something about which data is stored in a databank or database. For example, boundary and name. The data may consist of relationships, attributes, positional and shape information and so on. Often synonymous with feature. |
Extensible Markup Language (XML) | This is a markup language written in a textual data format designed to encode documents and data structures for transfer over the Internet. It was developed by the World Wide Web Consortium (W3C). XML schemas express shared vocabularies and allow machines to carry out rules made by people. They provide a means for defining the structure, content and semantics of XML documents. |
Extensible Stylesheet Language Transformations (XSLT) | This is a language for transforming XML documents into objects that can be presented in a format that is more easily read by the user, such as HTML for web pages or plain text. |
feature | An item of detail within a map that can be a point and/or symbol, text or line. |
feature identifier | A unique code to identify an individual feature. A specified part of a record containing a unit of data, such as the date of digitising. The unit of data may be a data element or a data item. |
feature record | The logical information, both spatial and attribute, describing a feature or entity. |
geographical information system (GIS) | A system for capturing, storing, checking, integrating, analysing and displaying data that is spatially referenced to the Earth. This is normally considered to involve a spatially referenced computer database and appropriate applications software. |
Geography Markup Language (GML) | GML was developed by the Open Geospatial Consortium (OGC), a global organisation of developers and users that aims to maximise the benefit of geographic information. GML is a spatially enabled dialect of XML schema. |
layer | A subset of digital map data selected on a basis other than position. For example, one layer might consist of all features relating to counties and another to wards. Also known as a level. |
level | A level corresponds to a single type of administrative unit, for example, a ward or a district, and is conceptual in form. See also layer. |
Line | A series of connected coordinated points forming a simple feature with homogeneous attribution. |
line feature | The spatial abstraction of an object in one dimension. Lines may intersect with other lines. They are defined as a series of two or more coordinate pairs and may be curved or straight. Curved lines consist of a series of very short straight-line segments. As an object abstraction, a line has no width. |
line segment | A vector connecting two coordinated points. |
link or edge | Links are the representation of line features. They are made up of one or more consecutive non-intersecting link segments with common attributes between two terminating nodes. Links have no connection with other links except at the start or end, via common (shared) terminating nodes (points). All links contain their terminating coordinates. Links may form the boundaries of polygons and may be shared between polygons. |
map scale | The ratio between the extent of a feature on the map and its extent on the ground, normally expressed as a representative fraction, such as 1:1250 or 1:10 000. |
name | The proper name or label of an object (real world) or feature (object abstraction). The descriptive name might consist of one or more text strings or be an attribute of the object or object abstraction. |
National Grid | A unique referencing system that can be applied to all Ordnance Survey maps of Great Britain (GB) at all scales. It is used by Ordnance Survey on all post war mapping to provide an unambiguous spatial reference in Great Britain for any place or entity, whatever the map scale. The National Grid is defined by the OSGB36 spheroid. |
Northings | See rectangular coordinates. |
object | A collection of entities which form a higher-level entity within a specific data model. |
object (real world) | A recognisable discrete part of the real world. |
origin | The zero point in a system of rectangular coordinates. |
point and line data | A form of vector data designed for map production in which all map features are designated as points, lines or text. Point and line data does not carry the topological relationships between features. |
polygon | Polygons are a representation of areas. A polygon is defined as a closed line or perimeter completely enclosing a contiguous space and is made up of one or more links. At least one node occurs on the perimeter of a polygon where the bounding link completes the enclosure of the area. There may be many nodes connecting the bounding links of a polygon. Links may be shared between polygons. Polygons may wholly contain other polygons or be contained within other polygons. |
polygon boundary | The link(s) which enclose a polygon, projected into the horizontal plane. A chain. |
record | A set of related data fields grouped for processing. |
rectangular coordinates | Also known as X Y coordinates and as eastings and northings. These are two dimensional coordinates that measure the position of any point relative to an arbitrary origin on a plane surface (for example, a map projection). |
resolution | A measure of the ability to detect quantities. High resolution implies a high degree of discrimination but has no implication as to accuracy. For example, in a collection of data in which the coordinates are rounded to the nearest metre, resolution is 1 metre, but the accuracy may be ± 5 metres or worse. |
segment | A chord defined by two consecutive coordinates in a line string. |
shapefile | This is a data format developed by Esri to describe features such as points, lines and polygons to enable spatial analysis. A shapefile consists of several files designed to hold information essential for the transfer of this data between software products which are capable of reading shapefiles. |
spatial data | Data that includes a reference to a two or three dimensional position in space as one of its attributes. It is used as a synonym for geometric data. |
spot height | A point on the Earth’s surface for which the height, above a reference datum, is known and which has been fixed by observation. |
String | A set of items which can be arranged into a sequence according to a rule. A sequence of coordinate pairs or triplets making up a line or a link. |
structured data | Data within which collections of features (of any type) form objects. Topographically structured data also contains topological information, defining the relationships between features and objects. |
Topography | The study of the physical features of the Earth. A topographic map’s principal purpose is to portray and identify the features of the Earth. |
Topology | The study of the properties of a geometric figure that are not dependant on position, such as connectivity and relationships between lines, nodes and polygons. |
Vector | A straight line joining two data points. |
vector data | Positional data in the form of coordinates of the ends of line segments, points, text positions and so on. |
spot_height |
land_water_boundary |
contour_line |
Fid | fid |
Id | id |
propertyValue | property_value |
propertyValue_uom | N/A |
spotHeightType | spot_height_type |
waterLevelCategory | water_level_category |
contourLineType | contour_line_type |
id | N | Y | Y | Y | Y | Y | Y |
property_value | N | Y | Y | Y | Y | Y | Y |
contour_line_type | N | Y | Y | Y | Y | Y | Y |
id | N | Y | Y | Y | Y | Y | Y |
property_value | N | Y | Y | Y | Y | Y | Y |
spot_height_type | N | Y | Y | Y | Y | Y | Y |
id | N | Y | Y | Y | Y | Y | Y |
property_value | N | Y | Y | Y | Y | Y | Y |
water_level_category | N | Y | Y | Y | Y | Y | Y |
Product name | OS Terrain 50 | gmd:MD_DataIdentification/gmd:citation/gmd:CI_Ci tation/gmd:collectiveTitle/gco:CharacterString |
Spatial representation | The structure of the data, either grid (DTM) or vector (contours) | gmd:MD_DataIdentification/gmd:spatialRepresentati onType/gmd:MD_SpatialRepresentationTypeC ode |
Tile reference | 10km National Grid tile reference | gmd:MD_DataIdentification/gmd:citation/gmd:CI_Ci tation/gmd:title/gco:CharacterString |
Topic category | INSPIRE theme: elevation | gmd:MD_DataIdentification/gmd:topicCategory/gmd :MD_TopicCategoryCode |
Coordinate reference systems | The projected coordinate reference system of British National Grid and the vertical reference system of Ordnance Datum Newlyn | gmd:MD_ReferenceSystem/gmd:referenceSystemIde ntifier/gmd:RS_Identifier/gmd:code/gmx:Anchor xlink:href="urn:ogc:def:crs:EPSG::27700"/British National Grid gmd:MD_ReferenceSystem/gmd:referenceSystemIde ntifier/gmd:RS_Identifier/gmd:code/gmx:Anchor xlink:href="urn:ogc:def:crs:EPSG::5701"/Ordnance Datum Newlyn |
Flying date(s) | The date that the area was flown by Ordnance Survey for revision. To accommodate multiple flying dates within the tile, two values will be recorded: the earliest flying date and the latest flying date present. Both dates can be identical. For Profile content, the Date Flown will be recorded as <null>. | gmd:MD_DataIdentification/gmd:extent/gmd:EX_ Extent/gmd:temporalElement/gmd:EX_Temporal Extent/gmd:extent/gml:TimePeriod /gml:beginPosition /gml:endPosition |
Processing date | The date the tile was created by Ordnance Survey; not the date of the real-world change or survey. | gmd:MD_DataIdentification/gmd:citation/gmd:CI _Citation/gmd:date/gmd:CI_Date/gmd:date/gco: Date |
Version number | An incrementing number to indicate the number of times the tile has been published. | gmd:MD_DataIdentification/gmd:citation/gmd:CI _Citation/gmd:edition/gco:CharacterString |
Reason for change | This provides information about the update to the data and whether it is a creation (new) or a revision (modified/verified), which is described in the metadata by using Lineage (see the following row in this table). | gmd:MD_DataIdentification/gmd:citation/gmd:CI _Citation/gmd:date/gmd:CI_Date/gmd:dateType/ gmd:CI_DateTypeCode |
Lineage | Text to describe the current status of the tile: ‘created from new imagery’, ‘some parts revised from new imagery’ or ‘new imagery examined and no change’. | gmd:DQ_DataQuality/gmd:lineage/gmd:LI_Lineag e/gmd:statement/gco:CharacterString |
<tile name>_line.shp
<tile name>_line.dbf
<tile name>_line.shx
<tile name>_line.prj
Esri shapefiles for contour and tide line data.
<tile name>_point.shp
<tile name>_point.dbf
<tile name>_point.shx
<tile name>_point.prj
Esri shapefiles for spot height data.
Metadata_<tile name>.xml
A metadata file for contour data, providing information on the flying date and so on.
<tile name>.gml
GML data file.
Metadata_<tile name>.xml
A metadata file for contour data, providing information on the flying date and so on.
