> 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/os-vectormap-district/os-vectormap-district-technical-specification/raster-specification.md).

# Raster Specification

The following chapters include information about OS VectorMap District raster, file compression, symbology, georeferencing and formats.

## **Specification**

* **Data Source:** Derived data
* **Number of tiles in Great Britain:** 2863 (edgematched)
* **Tile size:** 10km x 10km

Because digital maps frequently cover very large areas they are split down into squares known as tiles, each of which covers part of an overall area.

* **Availability:** National, country and tile supply available
* **Resolution:** 254 dots per inch
* **Data structure:** Raster
* **Data Specification:** Selection of map features combined
* **Colour Palette:** 256 fixed colours
* **Transfer format:** GeoTIFF (LZW\* compressed)
* **Storage Volume per tile:** Compressed: approx. 6.7mb
* **Greyscale:** A high-quality alternative to colour raster data is to use a GIS to convert data to a greyscale format.

\*If LZW compressed formats are used then registration may be required.

OS VectorMap District is supplied in the following raster formats: GeoTIFF (LZW compressed) (6.7mb)


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