# OS MasterMap Imagery Layer Technical Specification 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) --- # 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/os-mastermap-imagery-layer/os-mastermap-imagery-layer-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.