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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.
OS MasterMap data refresh dates
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.
OS MasterMap Topography Layer real-world object catalogue (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.
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.
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.
OS MasterMap user guide
Full supply and change-only update (COU) data will contain all of the themes in your contract area.
Do 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.
OS MasterMap user guide
When do changes in the real world get added to MasterMap Topography?
This depends on what Category the feature or change falls in - please see our Revision Policy for full details.
What are the advantages of TOIDs as a referencing system?
Each and every feature within OS MasterMap® has the TOID® as a unique reference. This makes it possible to identify any single feature within the dataset without any ambiguity. Current referencing systems, such as coordinates and addresses, are subject to interpretation between users. This creates fuzzy matching issues between organisations wanting to exchange data; for example, will the building St James House be picked up in another system where it is spelt St James' House?
TOIDs will stay the same throughout the life cycle of each feature. In other words, if a feature changes, the TOID will stay the same as long as it is deemed to be the same feature; for example, a house having an extension built is still the same house and fulfils the same purpose. This provides a continuity of reference even though a feature may undergo changes.
This makes the TOID a robust referencing system that customers can use alongside, or instead of, their own referencing systems and can link to their own information about the feature.
Having unique references is essential to making the most out of storing data within a relational database management system, as these rely on unique referencing to be able to store, sort, manage, query and retrieve data efficiently.