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Georeferencing is not required when using the GeoTIFF file format as the tiles have already been embedded with georeferencing information.
To be able to view each TIFF tile in correct geographic relation to the National Grid and to other tiles, the tiles must be georeferenced. Geographic information systems (GIS) typically provide georeferencing as part of their functionality, but for each set of tiles, it is necessary to provide the information on how the tiles should be ordered.
Ordnance Survey provides this information in a set of georeferencing files, also known as world files. A complete set of georeferencing files for 1:25 000 Scale Colour Raster is available to download free of charge from the Georeferencing files and land and sea tiles page of the OS website.
There are several different types of world file. Prior to downloading one of the sets, customers are advised to check with their system suppliers to find out which type of world file their system supports.
The conventions behind the files’ creation can be found in the product's technical specification. By using the conventions outlined there, this means that other datasets using the same conventions can be imported into the same GIS to add value to the raster map; for example, overlaying a routing or logistics network over the map or displaying a customer’s demographic information.
The georeferencing files should be saved in the same directory as the files of the map tiles themselves.
The data volumes for each file format are influenced by the level of data compression.
When an image is compressed, duplicated data that has no value is removed or saved in a shorter form, reducing a file’s size. For example, if large areas of water are the same tone, only the value for one pixel needs to be saved, together with the locations of the other pixels with the same colour. When the image is edited or displayed, the compression process is reversed. When raster data is compressed, not only are the data volumes reduced, but the user can download, display, edit and transfer images more quickly.
There are two forms of compression: lossless and lossy:
Lossless compression: As its name suggests, lossless compression does not lose information within an image. Lossless compression retains the original quality of an image when it is uncompressed. This process does not provide much compression, so file sizes remain large. Lossless compression is used mainly where detail is important, such as when planning to make large prints.
Lossy compression: This process degrades images to some degree, meaning that the decompressed image is not quite the same as the original. The more an image is compressed, the more degraded it becomes. In many situations, such as posting images on the Internet or printing small- to medium-sized prints, the image degradation is not so obvious. If a lossy compressed image is over-enlarged, the degradation will become apparent, and therefore, 1:25 000 Scale Colour Raster is not supplied using this form of compression.
TIFF is one of the most used lossless image formats. TIFF is primarily designed for raster data interchange and is supported by numerous image-processing applications. This permits much more efficient access to exceptionally large files that have been compressed.
ISO 19115 compliant UK GEMINI discovery level metadata is provided for the data and can be found on the AGI (The Association for Geographic Information) website.
The following list gives a detailed description of the metadata elements provided on the AGI website:
Title: The title of the product.
Abstract: The abstract gives a brief description of the product.
Currency: The currency takes the form of date of last update for the feature.
Lineage: The lineage metadata takes the form of product specification name and date of product specification.
Spatial extent: The spatial extent is supplied in the form of geographic identifiers (for example, England, Scotland and Wales) and in the form of geographic coordinates.
Spatial reference system: The spatial reference system for all products takes the form of a British National Grid system, namely OSGB36.
Data format: Data format takes the form of the name of the format or formats the product is supplied in.
Frequency of updates: Frequency of updates takes the form of a stated period of time.
Distributor’s contact details: Distributor contact details include postal address, phone number, email address and website.
Data originator: Given as the company having primary responsibility for the intellectual content of the data source; in all cases, this will be Ordnance Survey.
Other metadata available includes keywords, start date of data capture, access constraints, use constraints, level of spatial data, supply media and presentation detail
The image file directory for TIFF will contain a selection of the following entries:
File Byte Order: OS defaults to the use of MM = Motorola Byte Order; the order in which the data is interpreted.
Tag 256 (ImageWidth): The number of columns in the image, i.e. the number of pixels per row, for example, value = 4000.
Tag 257 (ImageLength): The number of rows of pixels in the image, for example, value = 4000.
Tag 258 (BitsPerSample): The number of bits per component, for example, value = 8.
Tag 259 (Compression): Compression scheme used on the image data, for example, value = 5 (LZW).
Tag 262 (PhotometricInterpretation): The colour space of the image data, for example, value = 3 (Palette).
Tag 270 (ImageDescription): A string that describes the subject of the image, for example, value = 1:25 000 TILE SU41.
Tag 273 (StripOffsets): For each strip, the byte offset of that strip, for example, first four values = 5640 19678 35692 51409.
Tag 277 (SamplesPerPixel): The number of components per pixel.
Tag 278 (RowsPerStrip): The number of rows in each strip, for example, value = 8.
Tag 279 (StripByteCounts): For each strip, the number of bytes in that strip after compression, for example, first four values = 14038 16014 15717 15442.
Tag 282 (XResolution): The number of pixels per Resolution Unit in the Image Width, for example, value = 254.
Tag 283 (YResolution): The number of pixels per Resolution Unit in the Image Length, for example, value = 254.
Tag 284 (PlanarConfiguration): Look-up table, for example, value = first four values = 22873 31354 39321 59110.
Tag 296 (ResolutionUnit): How the components of each pixel are stored. Default value is ‘2’ (inch).
Tag 306 (DateTime): Date and time of image creation, for example, value = 2007:06:30 12:38:41.
Tag 317 (Predictor): A mathematical operator that is applied to the image data before an encoding scheme is applied.
Tag 320 (ColourMap): Look-up table, for example, value = first four values = 22873 31354 39321 59110.
Tag 339 (SampleFormat): Specifies how to interpret each data sample in a pixel.
Tag 33432 (Copyright): Copyright notice, for example, value = ORDNANCE SURVEY CROWN COPYRIGHT 2019.
The preceding values are relevant to 1:25 000 scale TIFF data with LZW compression.
The legend for 1:25 000 Scale Colour Raster is available as a PDF download from the product page here.
The Welsh language legend for 1:25 000 Scale Colour Raster is available as a PDF download from the product page here.
The full tile list for 1:25 000 Scale Colour Raster is available as an excel sheet from the product page here.
The change-only update tile list for 1:25 000 Scale Colour Raster is available as an excel sheet from the product page here.
The purpose of this annex is to provide a glossary of terms used in the definition of products, services, licensing and other terms and conditions for 1:25 000 Scale Colour Raster.
A standard binary coding system used to represent characters within a computer.
The smallest possible unit of data, resulting from a choice between 0 and 1.
A boundary forms the division between two similar real-world objects, for example, property boundary or administrative boundary, and is defined by one or more lines.
A unit of computer storage of binary data, usually comprising 8 bits, equivalent to a character.
A distinctive mark; an inscribed letter; one of a set of writing symbols.
The binary representation of a single element of a character set; for example, EBCDIC, ASCII.
A coordinate pair is an easting and a northing.
A computational process of converting an image or map from one coordinate system to another.
Read-only memory (CD-ROM). A data storage medium. A 12-cm disc similar to the audio CD. It is an alloy disc pitted with tiny holes and then coated in plastic. A laser head reads the pattern of the holes and translates them into binary data.
The sole legal right to print or publish a work. Crown Copyright subsists in all Ordnance Survey publications for a 50-year period, from the end of the year in which they were first published, by virtue of the Copyright Designs and Patents Act 1988.
An organisation or individual that makes use of Ordnance Survey’s data supply facilities. This includes both direct sales customers of Ordnance Survey as well as customers of Licensed Partners. It does not include anyone, or any organisation, that has access to Ordnance Survey material without charge.
A representation of facts, concepts or instructions in a formalised manner suitable for communication, interpretation or processing.
An organised, integrated collection of geographic data, which may or may not be spatial data. It is stored so that specific applications can access the data by different logical paths. A database is accessed and managed by a database management system (software for managing database information).
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.
Attributes of a dataset that define its suitability for a particular purpose, such as completeness, positional accuracy, currency and so on.
The defined logical arrangement of data as used by a system for data management; a representation of a data model in computer form.
This is the means by which computer files are transferred from one computer to another. Transfer media may be subdivided into communications media and physical media.
Data as supplied in a particular format to customers, whether internal or external to Ordnance Survey.
A measure of the number of units of data held on a stated length of storage surface. For example, some magnetic tapes may be recorded at a density of 1,600 bits per inch (bpi). Often referred to as packing density.
The method of supply of data to a customer (such as offline and online).
A name describing a real-world object or feature (for example, School) as shown on the 1:25 000 Scale Colour Raster map.
The name as shown on the 1:25 000 Scale Colour Raster map.
Data that is expressed as numbers (digits) in computer-readable form.
The supply of revised digital data to a customer at a predetermined interval of time.
A direct transaction between Ordnance Survey and a customer.
A text feature which forms a name that distinguishes it from other text features of the same type, for example, Millbrook School.
The resolution, or fineness, of a raster image.
A data storage medium.
See rectangular coordinates.
An image named after the Joint Photographic Experts Group, which uses a lossy compression format. It is designed for compressing full colour or greyscale images of natural, real-world scenes and works well on photographs. It is the de facto standard for photographs on the web.
The process of converting information to a computer-readable form, for example, digitising maps.
A geographic entity such as a building or stream, either taken from a map or surveyed directly from the real world. Can be a point / symbol, text or line.
The specified arrangement of data, for example, the layout of a printed document, the arrangement of the parts of a computer instruction, the arrangement of data in a record.
The cartographic process of simplifying the depiction of features to fit the output scale. For example, road widening is necessary at smaller scales to enhance their visibility.
Assigning a geographic location to data, for example, adding coordinates to an address.
Coordinates, usually expressed as latitudes and longitudes, that define a point's position on the Earth's surface.
A definition for registering raster images within a geographic framework is the process of assigning map coordinates to the raster image data and resampling the pixels of the image to conform to the map projection grid.
GeoTIFF (Geographic Tagged Image File Format) is a public domain and OGC metadata standard. It is a TIFF image file with georeferencing information embedded in the file metadata. It can be utilised by a geographic information system (GIS). All GeoTIFF raster tiles are LZW compressed.
1 073 741 824 bytes, a measure of data storage capacity (see megabyte).
1,024 bytes, a measure of data storage capacity.
Any organisation that has entered into a formal licence agreement with Ordnance Survey to market map information or to incorporate map data with their application or service.
Map feature in the form of a line (for example, river and boundary) that may or may not represent a real- world (existent) feature.
The local origin of rectangular coordinates is the south-west corner of the 1 km by 1 km National Grid square they identify.
The ratio between the extent of a feature on the map and its extent on the ground, normally expressed as a representative fraction, for example, 1:1,250, 1:50 000 and so on.
1 048 576 bytes, a measure of data storage capacity (see gigabyte).
MapInfo format.
The metric grid on the Transverse Mercator projection used by Ordnance Survey on all post-Second World War mapping to provide an unambiguous spatial reference in Great Britain for any place or entity, whatever the map scale.
See rectangular coordinates.
The zero point in a system of rectangular coordinates.
In the 1:25 000 Scale Colour Raster product, a pixel is a single point represented by a square.
A pair of coordinates.
Attribute data expressed as an array of pixels, with spatial position implicit in the ordering of the pixels.
The real-world feature represented by a feature, for example, a building, a fence, a wood.
Also known as XY 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, a digitising table or a VDU screen).
Used to produce light or dark shading (for example, building / water fill); this is dependent on the spacing of the dots – the denser the dots, the darker the effect.
A set of items that can be arranged into a sequence according to a rule.
The file format in which the data is supplied to the customer.
MapInfo format.
Tags are unique numbers that are used for identifying specific information in TIFF files, for example, image width, image length, bits per sample, photo interpretation and resolution.
Character, or character string, or field or record used to signal the end of a record, or section, or volume or database.
A unit of map used to divide large areas into regular and more manageable sizes.
TIFF is a tagged image file format-based file format for storing and interchanging raster images with the most recent version (6.0) published in 1992.
The format used to transfer data between computer systems. In general usage, this can refer not only to the organisation of data but also to the associated information, such as attribute codes, which are required in order to successfully complete the transfer.
The physical medium on which digital data is transferred from one computer system to another. For example, compact disc.
An operating system that supports multitasking and is used by many workstations and minicomputers.
The process of adding to and revising existing digital map data to take account of change.
A physical unit of the transfer medium that is a single disk, or a single DVD.
This technical specification provides detailed technical information about 1:25 000 Scale Colour Raster. It is targeted at technical users and software developers.
The following pages contain information about 1:25 000 Scale Colour Raster, including file compression, legends, georeferencing and formats.
2,859 (edge matched)
England: 1,508
Scotland: 1,130
Wales: 289
10 km by 10 km
National coverage
254 and 660 dots per inch
Raster
TIFF PackBits compressed
TIFF palette 8-bit (256 colours) with LZW* compression
GeoTIFF with LZW* compression
0.2–9 Mb compressed
Quarterly: March, June, September and December (change-only updates)
Maintained versions (in English and Welsh) of the 1:25 000 Scale Colour Raster legend, which defines all of the map symbols used in the product, can be found on the 1:25 000 Scale Colour Raster Product Support page of the OS website:
This document contains additional theoretical information related to 1:25 000 Scale Colour Raster. All users will find the Product Information document useful and informative.
The 1:25 000 Scale Colour Raster data product mirrors the popular OS Explorer Map series, showing a detailed overview of environmental and leisure features across Great Britain. It can provide the ideal mapping backdrop upon which to overlay business information. The 1:25 000 Scale Colour Raster’s backdrop can then be overlaid with other Ordnance Survey vector products or a customer’s own geographic / business data; it can also provide a useful background map in its own right.
Screen images can be plotted to produce a high-quality map. An example of the data is shown below.
1:25 000 Scale Colour Raster is aimed at professional / business markets and its graphic specification can aid with the following:
Environmental applications
Leisure applications
Construction
Engineering
Planning and licence applications
Farm / estate / property management
Real estate
1:25 000 Scale Colour Raster is derived from the source data used to create its graphic counterpart, the OS Explorer Map series. Generalisation is used to emphasise, simplify, select and sometimes omit features to produce a cartographic representation of the landscape at a scale of 1:25 000.
The nominal scale of the product is 1:25 000, but the recommended minimum-to-maximum scale range is 1:8,000 to 1:25 000 scale.
1:25 000 Scale Colour Raster is available in National Grid coordinates, which are expressed in metres relative to an origin set to a point west of the Isles of Scilly. These coordinates can easily be spatially related to other surveys, drawings, datasets or Ordnance Survey products. A general introductory guide to the British National Grid (BNG) is available on the OS website.
Coverage is Great Britain only. 1:25 000 Scale Colour Raster is supplied in standard 10 km by 10 km tiles aligned to the National Grid.
1:25 000 Scale Colour Raster is updated via a revision programme. The revision programme mirrors that of the OS Explorer Map series, and is determined by assessing the following factors:
Known surveyed change
Change intelligence gathered from a range of sources
How long it's been since an area was last revised
Priority is given to prestige sites categorised as significant items of change, such as major road construction projects. Significant items of surveyed change relevant to the scale are captured during the revision programme.
Where a line feature ends by intersecting the tile edge, it is matched with its corresponding feature on the adjacent tile so that both features end on the same unique coordinate. The representation of detail across the tile edge will be of a cartographically acceptable standard when plotted or displayed at scale.
1:25 000 Scale Colour Raster is supplied to customers quarterly in March, June, September and December, incorporating any updates made by the revision programme.
1:25 000 Scale Colour Raster is the digital alternative to Ordnance Survey's OS Explorer paper map series for Great Britain available in 10 km square tiles. The 1:25 000 Scale Colour Raster’s backdrop can be overlaid with other Ordnance Survey vector products or a customer’s own geographic/business data or used as a standalone map.
This product is updated quarterly
1:25 000 Scale Colour Raster is the must-have map in any navigation app or device for hikers and cyclists. It depicts the landscape with detail and clarity that’s unsurpassed at this scale.
When you need map extracts for a consultation document, or a magazine for walkers, 1:25 000 Scale Colour Raster TIFF files can be opened and annotated in software like Photoshop and InDesign.
Tourist and heritage attractions of many types are shown on this mapping, so leisure app users can use it to find their way to a place of interest, whether it breaks up a day’s walking or keeps the kids amused on a rainy day.
660 dpi or 254 dpi
Palette of 256 colours
Along with a wide range of rights of way – footpaths, bridleways, National Trails and more – 1:25 000 Scale Colour Raster shows 'access land' that’s open to all. Thanks to this level of detail, visitors can enjoy the countryside and keep out of trouble.
This map can help you quickly and safely to incidents in remote areas. Field boundaries are included, along with contours, vegetation, scree and shoreline detail.
Access: Download
Data theme: Contextual
Data structure: Raster
Coverage: Great Britain
Scale: 1:25 000
Format: GeoTIFF, TIFF 8-bit LZW compressed, TIFF PackBits compressed
Ordering area: Customisable Area (10km2 tiles)
Publication months: March, June, September, December
OS Data Hub plan: Public Sector Plan, Premium Plan, Energy & Infrastructure Plan
You can try out a sample of OS MasterMap Topography layer data for evaluation and testing through the MasterMap Topography layer product page. Alternatively, you can try out the full product by applying for a Data Exploration license.
A definition for registering raster images within a geographic framework is the process of assigning map coordinates to the raster image data and resampling the pixels of the image to conform to the map projection grid. This allows tiles of map data to be located in their correct geographic position relative to the map projection and also to themselves.
Great Britain is surveyed and mapped using the Transverse Mercator (or Gauss-Kruger) projection, so all raster tiles will be mapped to this projection as it applies to Ordnance Survey National Grid if using world or TAB files supplied by Ordnance Survey.
Within the MapInfo format (MIF) record header, the following information will be found under COORDSYS:
CoordSys Earth Projection 8, 79, "m", -2, 49, 0.9996012717, 400000, -100000 Bounds(4.17232513428e
011, 7.7486038208e-011) (700000, 1300000)
This information relates to the Transverse Mercator projection, its position relative to the rest of the world and also an individual tile’s position relative to the projection. The record header is constructed as follows (not all fields have to be used):
| MIF record header component | Description |
|---|---|
1:25 000 Scale Colour Raster is available in Tagged Image File Format (TIFF) LZW, TIFF PackBits and Geographic TIFF (GeoTIFF) LZW compressed formats:
TIFF LZW (Lempel Ziv Welch) is a lossless compression (see the ).
TIFF PackBits is a lossless compression scheme that is supported by virtually all applications that can import TIFF graphics.
GeoTIFF LZW is a TIFF file which has geographic (or cartographic) data embedded as tags within it. The geographic data can then be used to position the image in the correct location and with precise geometry on the screen of a geographic information display.
TIFF is a file-based format for storing and interchanging raster images, with the most recent version (6.0) published in 1992.
There are two types of architecture for a TIFF. Many mainframe computers use what is known as a big endian (Motorola®) architecture. Most modern computers, including personal computers (PCs), use the little-endian (Intel®) system. 1:25 000 Scale Colour Raster TIFFs are supplied with Intel architecture.
Converting between these two systems is possible but, as a general rule, modern software should be expected to handle both of these outputs without operator intervention.
The 1:25 000 Scale Colour Raster conforms to the TIFF 6.0 standard. Customers are recommended to contact their system suppliers to ensure that their computer can read the Intel / little-endian TIFF architecture.
The GeoTIFF LZW compressed format is supplied as an online download which is available from the
. Other TIFF formats are also available from the OS Data Hub but as area of interest (AOI) downloads only (i.e. not as full supply).
The TIFF LZW and TIFF PackBits compressed formats are available for customers to request on DVD / HDD through .
The product is updated quarterly. OS Partners can select a full supply option or a change-only update (COU) option. Public Sector Geospatial Agreement (PSGA) customers are only able to select the COU option. If you select the COU option, then you will only receive tiles that have changed since the previous supply.
* If LZW compressed formats are used, then registration may be required. Information is available on the .
A full list of the is available on the OS website.
Completeness
Presence and absence of features against the specified data content*
Omission
Features representing objects that conform to the specified data content but are not present in the data
Commission
Features representing objects that do not conform to the specified data content but are present in the data
Logical consistency
Degree of adherence to logical rules of data structure, attribution and relationships
Conceptual consistency
How closely the data follows the conceptual rules (or model)
Domain consistency
How closely the data values in the dataset match the range of values in the dataset specification
Format consistency
The physical structure (syntax): how closely the data stored and delivered fits the database schema and agreed supply formats
Topological consistency
The explicit topological references between features (connectivity) – according to specification
Positional accuracy
Accuracy of the position of features
Absolute accuracy
How closely the coordinates of a point in the dataset agree with the coordinates of the same point on the ground (in the British National Grid reference system)
Relative accuracy
Positional consistency of a data point or feature in relation to other local data points or features within the same or another reference dataset
Geometric fidelity
The ‘trueness’ of features to the shapes and alignments of the objects they represent*
Temporal accuracy
Accuracy of temporal
Temporal consistency
How well-ordered events are recorded in the dataset (life cycles)
attributes and temporal relationships of features
Temporal validity (currency)
Validity of data with respect to time: the amount of real-world change that has been incorporated in the dataset that is scheduled for capture under current specifications
Thematic accuracy (attribute accuracy)
Classification of features and their attributes
Classification correctness
How accurately the attributes within the dataset record the information about objects*
CoordSys Earth Projection 8
The 8 relates to a MapInfo identifier, which in this case is the Transverse Mercator projection.
79
A MapInfo identifier; in this case, this relates to Ordnance Survey of Great Britain 1936, Airy ellipsoid.
“m”
This relates to the unit of measurement, which in this case is metres.
-2
This is the origin of the projection in respect of longitude.
49
This is the origin of the projection in respect of latitude.
0.9996012717
This figure indicates the distortion of the tile at the central meridian. A value of 1.0 would indicate no distortion at all. However, distortion within this projection is minimal, even at the far western or eastern limits.
400000, -100000
These figures indicate the false origin of the British National Grid. They represent the south-west corner of the Transverse Mercator projection which overlays Great Britain, so all coordinates for any tile, no matter what scale, will always be positive.
Bounds(4.17232513428e- 011, 7.7486038208e-011)
These values represent the minimum bounding X and Y coordinates for the tile.
(700000, 1300000)
These values represent the maximum bounding X and Y coordinates for the tile.
This page details the features depicted in the 1:25 000 Scale Colour Raster.
Buildings are generalised and shown with colour tint and cartographically placed text to indicate settlement name and extent.
Structures are indicated by lines, buildings or symbols, and selected distinctive named features are supplemented with a text description.
Transport features depicted include tracks, paths, roads, railway lines (single and multiple track), railway stations, airports and airstrips, ferry routes and ports, cycle routes, and bus and coach stations.
Water features are shown in blue with associated text. A distinction is made between natural (blue) and man-made (black) water features, except for canals (which are shown in blue).
Different types of natural features and vegetation are shown by symbols or colour tint, including woods, rock, scree, boulders, sand, shingle, mud and slope.
The following routes are depicted in this product:
Footpaths, including permissive
Bridleways, including permissive
Byways open to all traffic
Restricted byways
Other routes with public access (ORPA)
National Trails and Scottish Great Trails and Recreational Routes
Recreational routes
Rights of way (England and Wales only)
Access land
Portrayal of access land is intended as a guide to land that is normally available for access on foot, for example, access land created under the Countryside and Rights of Way Act 2000, and land managed by The National Trust™, Woodland Trust, National Parks and local authorities. Land owned by Forestry England is only shown as Open Access where coincident with CRoW land.
Ground contours, survey heights and air survey heights are depicted. Heights are to the nearest metre above mean sea level. Heights shown close to a triangulation pillar refer to the ground level height at the pillar and not necessarily the height at the summit.
National, county, district, unitary authority and civil parish boundaries are all depicted in the product.
Selected tourist and leisure information is normally restricted to features providing public access or services. Tourist information is shown by a blue symbol using, where possible, nationally recognised symbols. Where appropriate, symbols also have black distinctive names, for example, country parks, major gardens and so on.
Depiction includes information supplied by English Heritage®, the Royal Commission on the Ancient and Historical Monuments of Scotland, and the Royal Commission on the Ancient and Historical Monuments of Wales.
Low and high water, man-made and natural landscape features are all depicted.
National Grid lines are shown at 1-km intervals.
Descriptive and distinctive names are depicted as text.
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:
