# National Grid A 100km grid is provided as a separate layer. This is set as an invisible layer by default. The 100km grid is constructed from individual squares to enable them to be used easily for clipping and so on. A further non‑printing layer holds the 100km letter references to ease identification of the squares. For Illustrator users, the rulers have been set to match the zero point for National Grid. When the file is used at 1:1 000 000 scale and providing the rulers or page position have not been moved, the measurements can be used as National Grid coordinates (preferences must be set to millimetres). For example, the tip of Flamborough Head has an Illustrator coordinate of x = 525.85mm and y = 470.51mm, which corresponds to a National Grid reference of 5258 4705 (or TA 258 705); in Illustrator, the y value will be a minus value. ## National Grid coordinates for the raster versions The raster files have been provided for GIS users who might otherwise be unable to use the Illustrator or EPS files. The origin (lower-left corner) of the GB file is 0, 0 km and it finishes at 700km east and 1 300km north of the National Grid origin. This equates, at 254 dpi, to 7 000 pixels wide by 13 000 pixels high (100km = 1 000 pixels). ## Ireland and the Channel Islands Parts of the French and Irish coastlines have been included to help give context to the position of Great Britain. Although reasonably accurate, they use different map projections to GB and fall outside the National Grid. Their position and scale are therefore approximate. This also applies to the Channel Islands. ## Boundaries National, county and unitary authority boundaries are shown. County and unitary boundaries are depicted by the same style. Boundaries within the London Authority area are shown on a separate optional extras layer. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/miniscale/miniscale-technical-specification/national-grid.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.