A TOID ( TOpographic IDentifier, pronounced toyed) is a unique reference identifier assigned by the Ordnance Survey to identify every feature in Great Britain. The identifier consists of two parts, a prefix ‘osgb’ and a unique identifier that is 13-16 digits long. In GML 2, a TOID is encoded as a gml:fid (Feature Identifier); in GML 3 as a gml:id.
Around 440 million man-made and natural features have been thus identified: buildings, roads, fields, phone boxes, pillar boxes, landmarks and many other types. The identification system is designed to be used in GIS, digital cartography and in any customized computer application, including non-cartographic ones, where information about fixed, real-world features needs to be managed. Using consistent identifiers (IDs) makes it much easier to share data between various kinds of applications and systems. A TOID remains constant throughout the lifetime of the real-world feature it identifies, and is guaranteed not to be reassigned to anything else when the feature no longer exists.
Example: the TOID for the Tower of London is osgb1000006032892.