> 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-local/os-vectormap-local-overview/national-grid-coverage-for-os-vectormap-local.md).

# National Grid coverage for OS VectorMap Local

Ordnance Survey divides Great Britain into 100km x 100km squares. Each of these squares has a unique two-letter reference, for example, TG in the diagram below.

OS VectorMap Local tiles are identified by quoting the National Grid reference of the southwest corner of the 100km² area they cover, for example, TG.

<figure><img src="/files/TjXTSKl3Bf6VjsPmo1ov" alt="OS National Grid Reference System diagram. The diagram shows a map of Great Britain with 100km by 100km grid squares on top. Each square has a unique two-letter reference, e.g. TG. There is a black box around the TG square."><figcaption><p><em>OS National Grid reference system diagram.</em></p></figcaption></figure>

To describe an OS VectorMap Local raster format tile, which covers 5km x 5km, first add a two-digit reference to the 100km x 100km square reference, with the easting first followed by the northing, for example, TG23. This represents a 10km x 10km area which can be suffixed with a NE, NW, SE or SW to describe the 5km x 5km tile.

<figure><img src="/files/E2O1K6nsomLgDonucEp7" alt="" width="414"><figcaption><p><em>100km x 100km square reference TG in the OS National Grid reference system.</em></p></figcaption></figure>

A [general introductory guide to the British National Grid (BNG)](https://getoutside.ordnancesurvey.co.uk/guides/beginners-guide-to-grid-references/) is available on the OS website.


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