# GB Overview Maps Technical Specification Ordnance Survey's GB Overview Maps are a pair of small-scale maps designed predominantly for screen use. They provide geographic context for the whole of Great Britain by showing the major boundaries, a spread of towns and cities, hill shading, road networks and national parks. GB Overview Maps are derived from our MiniScale data and supplied in raster format (GeoTIFF). The raster files can also be used for web applications or within a geographical information system (GIS) as a backdrop. GB Overview Maps are most suited for viewing on screen, but can also be used for simple publications. ## **Product Specification.** ### **Files** 2 single TIFF image files, one for each map. ### **Coverage** Great Britain ### **Availability** National coverage (in a single download) ### **Scale** 1: 5 000 000 ### **Resolution** 254 dots per inch (dpi) ### **Data structure** Raster ### **Storage volumes (Great Britain coverage)** * 2,148 KB (compressed) GB Overview * 2,902 KB (compressed) GB OverviewPlus ### **Update frequency** Annually (January) ### **Coordinate reference system** British National Grid (OSGB36) ### **Additional technical information** Technical information common to all of the colour raster map family of products is available on the [Colour Raster Map Fundamentals page](/os-downloads/products/maps-and-imagery-portfolio/maps-and-imagery-fundamentals.md). These pages provide an overview of the product and a technical specification covering: * [Georeferencing](https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/colour-raster-map-fundamentals/colour-raster-map-technical-specification/georeferencing) * [Image file directory (TIFF)](https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/colour-raster-map-fundamentals/colour-raster-map-technical-specification/image-file-directory-tiff) * [Product glossary](https://docs.os.uk/os-downloads/products/maps-and-imagery-portfolio/colour-raster-map-fundamentals/colour-raster-map-technical-specification/product-glossary) --- # 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/gb-overview-maps/gb-overview-maps-technical-specification.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.