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OS MasterMap frequently asked questions

Where can I get a historic view of OS MasterMap®?

Ordnance Survey does not hold archives or historic views of OS MasterMap data.

If you have been directly licensed by Ordnance Survey to use OS MasterMap data over a continuous period of time, and have accumulated data during this period, you may hold and use it to provide historic views so long as you continue to remain directly licensed for the data by Ordnance Survey.

If you are not a licensee and wish to view and undertake limited copying of historic versions of OS MasterMap data, then you may do so at one of the six Legal Deposit Libraries that hold annual 'snapshots' of large-scale Ordnance Survey data, which Ordnance Survey voluntarily deposits by Agreement with these Libraries. The data may only be accessed within the premises of one of these Libraries, and views and prints made from the data may only be used for purposes included within the exceptions to the Copyright Designs and Patents Act 1988.

The six Legal Deposit Libraries are: The British Library; The Bodleian Library, Oxford; Cambridge University Library; The National Libraries of Scotland and Wales; and the Trinity College Library, Dublin.

How many unique feature types/feature codes are in OS MasterMap?

There are seven feature types within OS MasterMap Topography Layer:

Topographic point
Topographic line
Topographic area
Boundary line
Cartographic symbol
Cartographic text

There are 92 feature codes, which are made up of three attributes – the feature type, descriptive group and descriptive term.

How often is OS MasterMap updated?

The survey data that is used to create OS MasterMap is captured on a daily basis by both field survey and from aerial photography. The data has to go through a number of different databases and production processes before it can be released to the customer. This means that the database from which customers are supplied is actually refreshed every six weeks.

How can I notify you of any errors or omissions in OS MasterMap?

We are always pleased to accept information from our customers that will help us to improve the quality of our data. Please forward, with as many details as possible including a postcode, co-ordinates or TOID reference, errors or omissions to customerservices@ordnancesurvey.co.uk or via the post to Ordnance Survey, Adanac Drive, Southampton, SO16 0AS or telephone 08456 05 05 05.

Will the tile reference system be used for ordering OS MasterMap?

OS MasterMap is not a tile-based product. Using the OS MasterMap online service you can order exactly the features you require by defining an area of interest. Alternatively, you can order from a list of predefined polygons, you can import a tile list or we can import your own polygons (subject to restrictions).

What is the difference between GZ and GML format?

GML data is supplied in a compressed format called GZIP, which is denoted by the '.gz' filename suffix. Compression using the GZIP algorithm allows OS MasterMap data volumes to be reduced by a ratio of between 20:1 and 30:1.

My system reads NTF directly. Do I need a translator for all layers?

You will need a GML translator for all layers apart from OS MasterMap Imagery Layer. Please contact your system supplier or refer to the list of suppliers available at the systems and software page for further information.

What is a feature validation dataset (FVDS)?

The FVDS enables OS MasterMap users to verify their data holding. It is a list of TOIDs with their corresponding version number and version date. There is an option on the OS MasterMap online service to take a FVDS for an order.

I can't find data in the directory folders I would expect to? Is it missing?

Because of the way OS MasterMap GML files are named in an order, it can appear at first glance that only certain areas of data have been supplied.

The polygon that you submit within order for OS MasterMap data can create a situation where the data is supplied in a different folder to the one you may have expected.

This is due to the use of a ‘floating chunk grid’. This is specific to the order polygon and does not use a regular pattern of fixed tiles.  This chunking grid has been used to ensure data is supplied with the minimum amount of separate files.

The OS MasterMap ‘chunks’ will be created using the size of chunk you have selected as part of the ordering process.

For example, if you order data for SU7325 and SU7425 the folder on the OS MasterMap order will be named to the SW corner of the 5km x 5km chunk that contains those tiles. In this case, the single file name will include the National Grid reference of  SU7325 but will also contain the data for SU7425.  The next GML folder if applicable to the order would then have SU7825 as part of its file name, which will be 5km on from the first chunk.

Therefore, if you cannot find the data in the folders you are expecting to find them in, please open other folders in the correct National Grid sequence applicable to your chunk size to check the contents.

Can CAD systems use OS MasterMap Topography Layer?

Many suppliers of CAD (computer-aided design) systems have, or are in the process of developing, the technology to translate OS MasterMap Topography Layer data directly into their systems.

There are also third party suppliers of translators that can translate the native format .gz or .gml data into CAD formats. If your organisation is already using Topography Layer, check whether the translator you currently use can translate into the CAD formats you require.

There is a range of methods for translating OS MasterMap Topography Layer data; the appropriate one for you depends upon how you currently hold the data, whether you wish to convert from the Ordnance Survey supplied data or you may wish to export from your corporate holding.

Can the Topography Layer be turned into  DXF™ files?

 

Using a CAD system, OS MasterMap Topography Layer can be split into DXF layers using the feature code attribute in both products.

If you wish to use these additional features you should check that your translator can deal with them. Most translators split the OS MasterMap Topography Layer into one layer per unique feature code. If this is the case, use the look-up table to identify the layers that contain the new features.

Where can I learn more about CAD translators and solutions?

A variety of CAD (computer-aided design) solutions and translators are available from our partners. Some act as plug-ins to existing environments whilst others are translators that import and export data in various formats.

Different functionality is available from different options.

Some functions you may consider useful include:

  • ability to cut output into tiles;
  • processing of multiple chunks – removal of duplicate features at edges;
  • processing and creation of area features in addition to lines, text and point features;
  • COU (change-only update) incorporation;
  • flexible options to process and output only selected features;
  • direct access to centrally held data (database holding or GIS native files holding);
  • interface offering area selection; and
  • batch process conversion.

Ordnance Survey has a policy of not recommending or accrediting software. You are encouraged to contact partners directly to ascertain if their software or services fit your requirements. Please consult our list of OS MasterMap system suppliers for further information.

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