OS Master Map

OS Master Map

OS MasterMap® is Ordnance Survey's flagship digital product, launched in November 2001. It is a database that records every fixed feature of Great Britain larger than a few metres in one continuous digital map. Every feature is given a unique TOID (TOpographical IDentifier), a simple identifier that includes no semantic information. Typically each TOID is associated with a polygon that represents the area on the ground that the feature covers, in National Grid coordinates. OS MasterMap is offered in themed "layers", for example a road layer and a building layer, each linked to a number of TOIDs. Pricing of licenses to OS MasterMap data depends on: the total area requested, the layers licensed, the number of TOIDs in the layers, the period in years of the data usage.

OS MasterMap can be used to generate maps for a vast array of purposes. Although the scale on a digital map is much more flexible than a paper map, one can print out maps from OS MasterMap data with detail equivalent to a traditional 1:1250 paper map.

Ordnance Survey claims that OS MasterMap data is never more than six months out of date, thanks to continuous review. The scale and detail of this mapping project is so far unique. Around 440 million TOIDs have so far been assigned, and the database stands at 600 gigabytes in size. OS MasterMap is currently (August 2005) at version 6.

Ordnance Survey is encouraging users of its old Land-Line data to migrate to OS MasterMap.