> 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/1-250-000-scale-colour-raster/1-250-000-scale-colour-raster-technical-specification.md).

# 1:250 000 Scale Colour Raster Technical Specification

This technical specification provides detailed technical information about 1:250 000 Scale Colour Raster. It is targeted at technical users and software developers.

## 1:250 000 Scale Colour Raster product specification

### Number of tiles in Great Bitain

56 (edge matched)

### Tile size

100km by 100km

### Coverage

Great Britain

### Availability

National coverage (in a single download)

### Resolution

254 dots per inch (dpi)

### Data structure

Raster

### Storage volumes (Great Britain coverage)

* 128 MB (compressed)
* 130 MB (uncompressed)

### Update frequency

Annually: June

## Product legend <a href="#bookmark1" id="bookmark1"></a>

Maintained versions (in English and Welsh) of the 1:250 000 Scale Colour Raster legend, which defines all of the map symbols used in the product, can be found on the [1:250 000 Scale Colour Raster Downloads page.](/os-downloads/products/maps-and-imagery-portfolio/1-250-000-scale-colour-raster/1-250-000-scale-colour-raster-downloads.md)

## Gazetteer <a href="#bookmark2" id="bookmark2"></a>

The 1:250 000 Scale Gazetteer includes approximately 25 500 points that cover the extent of the 56 100km by 100km tiles. The information is provided as a single file in ASCII text format and is included in the compressed download file.

## Additional technical information

Additional information, common to all colour raster map products is available through the Colour Raster Map Fundamental 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)
* [Product glossary](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals/maps-and-imagery-products-technical-specification/product-glossary.md)


---

# 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 by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/1-250-000-scale-colour-raster/1-250-000-scale-colour-raster-technical-specification.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.