OS MasterMap Topography Layer support


The Topography Layer is the most detailed, current and comprehensive map dataset of Great Britain. You can reference your data with it to any real-world feature, helping you to manage your organisation's assets more effectively.

Schema 9 and OS data fulfilment

The Schema 9 upgrade to OS MasterMap Topography Layer and OS MasterMap Integrated Transport Network Layer was released in March 2017. We also went live with an upgraded data fulfilment system. Learn more

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.

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.

The update of real world features within OS MasterMap Topography Layer depends on which category of change the feature falls in, as described in our Basic scale revision pollcy.

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

Please see the real-world object catalogue (12 Mb PDF), which lists every type of real-world object in the OS MasterMap Topography Layer specification, and details how it is represented by Topography Layer features.

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 accurate is OS MasterMap Topography Layer?

We define accuracy in three ways:

Absolute accuracy – how closely the coordinates of a point in the dataset agree with the coordinates of the same point on the ground (in the British National Grid reference system).

Relative accuracy – positional consistency of a data point or feature in relation to other local data points or features within the same or another reference dataset.

Geometric fidelity – the ‘trueness’ of features to the shapes and alignments of the objects they represent when testing the data according to the dataset specification against the ‘real world’ or reference dataset.

The following table represents the absolute and relative accuracy applicable to the scale at which the product was surveyed.

Original survey scale 99% confidence level 95% confidence level RMSE*
Absolute Accuracy 0.9 m 0.8 m 0.5 m
Relative Accuracy +/- 1.1 m (up to 60 m) +/- 0.9 m (up to 60 m) +/- 0.5 m (up to 60 m)
Absolute Accuracy 2.4 m 1.9 m 1.1 m
Relative Accuracy +/- 2.5 m (up to 100 m) +/- 1.9 m (up to 100 m) +/- 1.0 (up to 100 m)
1:10 000
Absolute Accuracy 8.8 m 7.1 m 4.1 m
Relative Accuracy +/- 10.1 m (up to 500 m) +/- 7.7 m (up to 500 m) +/- 4.0 m (up to 500 m)

*RMSE (root mean squared error) is the square root of the mean of the squares of the errors between the observations.

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 (PDF).

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

Do Topography Layer boundaries represent legal property extents?

No, OS MasterMap Topography Layer doesn't show 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 (PDF) for further information.

How does OS distinguish between attribute change and physical change?

OS provides the answer to this question in the ‘Reason for change’ attribute:

If the attribute of the feature have changed the ‘Reason for change’ attribute would be Reclassified.

If the geometry of the feature changed (the feature has been edited by an operator) the ‘Reason for change’ attribute would be Modified.

When both attribute and geometry have changed, the ‘Reason for change’ would be also Modified.

What are the advantages of TOIDs as a referencing system?

Each and every feature within OS MasterMap® has the TOID® (TOpographic IDentifier) 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.

Where can I find details of the Topography Layer upgrade?

Please see our guide to the changes, where you can learn about the new content, styling options and more.

How do I obtain OS MasterMap Topography Layer – Building Height Attribute?

Building Height Attribute is an enhancement to and forms part of the OS MasterMap Topography Layer, so you are entitled to obtain Building Height Attribute without additional charge if you hold a current license for OS MasterMap Topography Layer.

Members of our public sector mapping agreements may log in and download alpha data for England and Wales and Scotland. Customers who order Topography Layer directly from Ordnance Survey should contact our Customer Service Centre or their Account Manager for more information. If you obtain your OS MasterMap Topography Layer data holdings via a Partner, please contact them.

If you aren't currently a customer, you can still download a small area of BHA sample data.

How often will Building Height Attribute data be updated?

As OS MasterMap Topography Layer - Building Height Attribute is an alpha release, the data is not currently maintained. However, we are continuing to expand the amount of coverage that is available. 

The third alpha release of Building Height Attribute was released in early December 2014.  It expanded the coverage to over 11,000km2 of urban areas and included attribution for some rural areas.

We aim to use customer and partner feedback from this alpha release to further develop the attribution, with an intention that in future it will be incorporated into the wider OS MasterMap Topography Layer specification and be supplied and maintained as a part of the Topography Layer.

What file format is Building Height Attribute available in?

In order to supply Building Height Attribute to customers quickly, we will initially supply this attribution as a comma delimited (.csv) file, which can be joined to OS MasterMap Topography Layer using the TOID. There are instructions to help you with this process in the Getting Started Guide.

We aim to use customer and partner feedback from this first alpha release to further develop this attribution, with an intention that in future it will be incorporated into the wider OS MasterMap Topography Layer specification and be supplied in GML as a part of the Topography Layer.