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.