> 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-mastermap-imagery-layer/os-mastermap-imagery-layer-technical-specification.md).

# OS MasterMap Imagery Layer Technical Specification

This technical specification provides detailed technical information about OS MasterMap Imagery Layer. It is targeted at technical users and software developers.

OS MasterMap Imagery Layer adds a visual and contextual capability to the other OS MasterMap Layers and OS data. Ordnance Survey has set the specification and quality levels for the OS MasterMap Imagery Layer with the aim of providing a reliable and consistent source of orthorectified aerial photography for general business use in Great Britain.

The technical specification contains details on the visual appearance of the ortho images within the imagery layer. It includes positional and geometric fidelity requirements and detail on mosaicing and edgematching between areas of imagery collected at different times.

In addition, this specification provides information on Georeferencing, Header files and product Metadata.

## Index

* [Image appearance](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-imagery-layer/os-mastermap-imagery-layer-technical-specification/image-appearance.md)
* [Ancillary files](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-imagery-layer/os-mastermap-imagery-layer-technical-specification/ancillary-files.md)


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