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OS MasterMap Topography Layer frequently asked questions

How often is the OS MasterMap Topography Layer updated?

All OS MasterMap® datasets are created from a single master dataset, which is refreshed regularly. Currently, the refresh period for Topography Layer supply is every six weeks.

The OS MasterMap Topography Layer works on the principle that you will take an initial supply of all data in your area of interest and then update the data by taking change-only update (COU).

COU brings your dataset up to date with the most recent OS MasterMap data available from Ordnance Survey.

Go to OS MasterMap data refresh dates page

How can I find out if a certain type of real-world object is represented in the Topography Layer?

The real-world object catalogue lists every type of real-world object in the OS MasterMap Topography Layer specification, and details how it is represented by Topography Layer features.

Open the OS MasterMap Topography Layer real-world object catalogue PDF (12 Mb)

Additionally a Feature Catalogue is provided showing the feature types idenifiable in the data, there attributes and examples of what they look like in the data and in the real world.

Open the OS MasterMap Topography Layer feature catalogue


What scale is OS MasterMap Topography Layer data?

For cartographic representation, OS MasterMap Topography Layer is captured and designed for display at 1:1250, 1:2500 and 1:10 000 scales in urban, rural and mountain/moorland areas respectively. In GIS OS MasterMap can be viewed over a considerable range of scales. The most scale-sensitive feature types, such as cartographic text and symbol features, are fixed in size and rapidly become less clear at smaller display scales (that is, when zoomed out).

OS MasterMap Topography Layer is also suitable for use in non–cartographic applications where the concept of scale is less applicable.


How do I order OS MasterMap Topography Layer?

Orders and estimates for all OS MasterMap layers and themes are made using the online ordering and supply service.

Go to the OS MasterMap online service page for further details

What are OS MasterMap Topography Layer themes?

In OS MasterMap Topography Layer, features are grouped into themes, such as buildings, land and water and so on, to enable more flexible data selection by customers. The rules that dictate which theme a feature becomes part of are governed by the classification attributes of the feature. These rules are in OS MasterMap Topography Layer themes chapter of the user guide.

Go to the OS MasterMap user guide page

Full supply and change-only update (COU) data will contain all of the themes in your contract area.


Does OS MasterMap Topography Layer boundaries represent legal property extents?

No, they do not. OS MasterMap Topography Layer gives no information on land and property ownership.


How do I determine the captured accuracy of a feature (capture scale)?

For topographic area features in OS MasterMap Topography Layer, it is necessary to look at the accuracy of position attributes of the topographic line features, which form the boundary of the area feature polygon. Please see the user guide for further information.

Go to the OS MasterMap user guide page

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For general enquiries, complaints, feedback or suggestions, email: customerservices@ordnancesurvey.co.uk or call us on 08456 05 05 05