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OS MasterMap revision policy

This is our policy for updating large-scale data. The product most directly affected is OS MasterMap Topography Layer.


As the national mapping agency of Great Britain, Ordnance Survey maintains around 234 000 km² of topographic information, ranging from dense urban conurbations to mountain and moorland areas. We want you to benefit from the most up-to-date mapping, therefore it's essential we regularly update our data.

We constantly strive to improve the quality, accuracy and content of our products. We value the feedback we receive from formal market research, customer seminars and directly through our account managers. We welcome input and comment on revision policy and any other aspect of our activities.

Details of the policy

Revision activity is split into two processes: continuous revision and cyclic revision.

Continuous revision is undertaken for those features of most importance to the majority of customers – mainly built development such as new houses and roads. We aim to capture these features within six months of construction being completed on the ground.

Cyclic revision is undertaken periodically mainly for changes to the natural environment, which tend to be slower and less evident than additions to the built environment. This information is of use to many customers, with certain areas surveyed purely in the national interest. Capture can be most economically achieved using systematic revision at fixed intervals, typically through aerial photography.

Under the current revision policy, our priorities when capturing new detail are based on the following categories.

Currency of categories of change

This section defines the timescales for capture of real-world change. The classification of real-world change is described below.

Definition of categories of change

Definition of a site

A site is defined as a self-contained location for an identifiable purpose, for example, a retail outlet, a flat, a local authority office, a group of agricultural buildings, an industrial unit, a pumping station and so on.

Sites may consist of a single feature, for example a communications mast, or more commonly, two or more area features. Sites may lie spatially within other sites, for example, an electricity substation within the grounds of a hospital.

NOTE: This covers the general definition of a site within OSMasterMap not the features within OSMasterMap Topography Layer-Sites product.


Further details about the categories of change, including the criteria for each section.

Further information on categorisation of change

This section provides further guidance and clarification on the categorisation of change.