OS Maps API (WMTS)
The OS Maps API is a base mapping product provide by Ordnance Survey via the OS DataHub.
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 from Bluesky Mapshop which is free for every local authority.
Using the OS Maps API in iShare
In order to use the OS Maps API as a Basemap in iShare you need to be on v6.0.0 of iShare which uses MapProxy (instead of Tilecache) as it supports WMTS. Please see Using MapProxy to proxy a WMTS Basemap for details.