> 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/1-50-000-scale-colour-raster/1-50-000-scale-colour-raster-technical-specification.md).
# 1:50 000 Scale Colour Raster Technical Specification
This technical specification provides detailed technical information about the 1:50 000 Scale Colour Raster. It is targeted at technical users and software developers.
## 1:50 000 Scale Colour Raster product specification
### Number of tiles in Great Britain
820 (582 sea tiles)
### Tile size
20km by 20km
### Availability
National coverage
### Resolution
254 and 660 dots per inch
### Data structure
Raster
### Transfer format
* TIFF-PackBits
* TIFF-LZW
* GeoTIFF
* Windows\*\*®\*\* BMP
### Storage volumes per tile
0.3–18 Mb
### Update frequency
Quarterly: March, June, September and December (change-only updates)
## Product legend
Maintained versions (in English and Welsh) of the 1:50 000 Scale Colour Raster legend, which defines all of the map symbols used in the product, can be found on the [1:50 000 Scale Colour Raster Downloads page](/os-downloads/products/maps-and-imagery-portfolio/1-50-000-scale-colour-raster/1-50-000-scale-colour-raster-downloads.md).
## Common mapping abbreviations used in the product
A full list of the common mapping abbreviations used in 1:50 000 Scale Colour Raster is available from the [Abbreviations used on OS 1:25 000 and 1:50 000 scale mapping page](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/abbreviations-used-on-os-1-25-000-and-1-50-000-scale-mapping.md).
## Additional technical information
Additional information, common to all colour raster map products is available through the Colour Raster Map Fundamentals pages. These pages provide an overview of the product and a technical specification covering:
* [Georeferencing](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/georeferencing.md)
* [Image file directory (TIFF)](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/image-file-directory-tiff.md)
* [Abbreviations used on OS 1:25 000 and 1:50 000 scale mapping](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/abbreviations-used-on-os-1-25-000-and-1-50-000-scale-mapping.md)
* [Product glossary](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/product-glossary.md)
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