The OS Maps API provides accurate, up-to-date maps that offer the most convenient way to add detailed OS data to your application. This allows you to make location-based decisions with confidence, removing the overhead of managing complex datasets yourself.
There are four styles available: Road, Outdoor, Light and Leisure. Each map style contains OS OpenData and Premium data layers. From iShare v6.0.0 these can be used as Base Maps for iShare Maps or iShare GIS.
OS Maps API serves pre-rendered raster tiles and is available in two projections; British National Grid for GB data and Web Mercator which is a global coordinate system. You can request the maps using the Open Geospatial Consortium Web Map Tile Service (WMTS) standard or RESTful ZXY. WMTS is supported by most GIS software and ZXY is efficient for web mapping.
The OS Maps API is free under your PSGA (Public Sector Geospatial Agreement) but you will need to generate a Project API Key and URL in order to access the WMTS.
Also under your Geospatial Agreement you will have access to Aerial Photography which is free for every local authority.