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Ordnance Survey (OS) have been using computers to help draw their maps since the late 1960s and the use of digital mapping techniques, both in survey and production has gradually replaced more traditional methods.

By 1995-6 all large-scale mapping had been digitised and in 1997 publication of large-scale mapping ceased. Since then all large-scale mapping has been available through “print-on-demand” only. At the same time the OS ceased to provide microfilm updates to the Legal Deposit Libraries.

In order to fill the gap an agreement was made between the OS & the Legal Deposit Libraries to provide access to the digital data. As a result of this agreement the Library has been receiving annual snapshots of OS Land-Line® data since 1998. This data was made available to readers on a standalone machine and users could obtain a black and white printout of the data.

The OS have now changed the way that they present their data to users and have a new product called OS MasterMap®. A new agreement between OS and the Legal Deposit Libraries means that this new product is now available in the Library.

From 2006, the OS MasterMap® Topography Layer has been received, updated by a new snapshot each year on an ongoing basis. All annual snapshots from 1998 onwards can now be explored and compared using the same Viewer.

OS MasterMap® offers improved layers of information, allowing more precise recording of landscape change over time. The system can be viewed in the South Reading Room and a limited number of customised A4-sized colour printouts of any area can be made for private, non-commercial use.