# Theme definitions A theme is a set of features that have been grouped together for the convenience of customers and to provide a high-level means of dividing the data in the layer logically. Features belong to only one theme. Below are descriptions of the themes that are currently included in OS MasterMap Sites Layer and examples of functional sites that are represented within these themes. Also provided is an explanation of the features included or excluded during the capture process of an extent. OS MasterMap Sites Layer provides seven themes: * [Air transport](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/air-transport.md) * [Education](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/education.md) * [Medical care](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/medical-care.md) * [Rail transport](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/rail-transport.md) * [Road transport](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/road-transport.md) * [Water transport](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/water-transport.md) * [Utility or industrial](/os-downloads/products/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions/utility-or-industrial.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/land-and-terrain-portfolio/os-mastermap-sites-layer/os-mastermap-sites-layer-technical-specification/theme-definitions.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.