Ordnance Survey – Great Britain's national mapping agency
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Link files and statistics
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Link Files Data Licence
Ordnance Survey is willing to license the Link File Data to customers and partners only on the condition that they accept all the terms contained in the Link File Data Licence agreement ("Licence") and their existing licence agreement(s) with Ordnance Survey (Existing Licence Agreement(s)). Use of the link files is limited to the scope of use set out in the same documents. By accessing the link files data you are confirming your acceptance of the terms of the Link Files Data Licence. It is unlawful to load the Link File Data into a computer without accepting this Licence.Link Files Data Licence
Link file improvements - June 2006
Ordnance Survey completed the PAI programme in March this year. Since then we found a section of one link file where the links could be improved. On discovering this we undertook a wider review and have earmarked 2320 files that could benefit by further enhancement.
It should be noted that it is just the link files that are to be enhanced, the underlying data itself is of good quality.
All customers who possess large scale data in affected areas have been written to. Our recommendation is to hold off migrating data in these areas until supplied with the improved links if their conversion process is using links, which not all are. Should they be in any doubt we are also recommending they contact either Ordnance Survey or their system/service provider.
The aim was to have all the improvements done by the end of September 2006 but in fact we have managed to get everything done for the August Release. Initially we thought the links from the 'Rural Town' Mablethorpe needed enhancing but this is not the case and the 16 files have been removed from the programme. As soon as the new links become available they will be posted on the ftp server (affected files are being removed) and improved links will be sent to customers on a monthly basis.
The list of affected links files (119KB) is provided and this will be maintained throughout the improvement process. August improvements now available
Link file statistics – March 2006
This file contains statistics for link files created as part of the Positional Accuracy Improvement (PAI) programme. There is a worksheet for each 100 km by 100 km square (SU, TQ and so on) and the statistics are arranged in alphanumeric order.
HP to OV (5..55 Mb)
SD to SK (4.3 Mb)
SM to SZ (6.6 Mb)
TA to TV (3.92 Mb)
Introduction to Link Files
Link files are supplied for every positional-accuracy improved 1:2500 scale map tile that is resupplied to Land-Line® customers holding a maintenance agreement, and to customers taking delivery of OS MasterMap®. Each link file is in comma separated value (.csv) format and contains the coordinates (in metres) of both the original and the new position of selected="selected" points together with the feature code that is related to that detail point.
Old position (eastings and northings), new position (eastings and northings),
feature code
Record example: 457224.20,0221147.60,457223.39,0221146.11,0030
As a direct result of feedback from customers and software developers, we have refined the process for creating links. Improvements have been made on the density and distribution of the links and the number of zero vector links has been increased. There are also links on features that have had a real-world change, for example, if a building has had an extension, the corners that have not changed could be linked. Improvements have also been made on the number of links on linear features such as roads, pavements and field boundaries. We have also sought to limit the number of rogue links, but we realise that despite rigorous quality assurance some rogues may still exist.