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
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.
Link files contain before and after coordinate positions of points on a map tile and the feature code of the feature to which the link relates. They have been developed to be used with appropriate transformation software as an aid to moving customers' data in accordance to any shift patterns that have occurred in the map data as a result of positional accuracy improvement (PAI).
When you apply the link files and your chosen third party rubber sheeting software, you are advised to:
- Optimise any parameter variables that are available within the software to obtain the most effective result for your data.
- Set up a quality assurance system to confirm that the results from the transformation process are satisfactory to your business needs.
- Transform your data only once.
Link files and data transformation
Link files are only effective for the map area they cover so do not include any feathered data in the collar tiles to a PAI block. Each link file is titled by the south-west corner of the National Grid square that it covers.
In setting up transformation software, organisations will need to decide how they wish their data to be presented at the edge of the improved area. Much of this will depend on:
- the options in the way in which data can be handled at tile edges by the transformation software;
- the accuracy of the current data;
- the quality, quantity and type of an organisation’s data assets;
- the quality assurance processes that are needed to inspect the data after transformation;
- the amount of time the data, or a portion of it, can be withheld from general use;
- the use to which the data is put;
- the correlation between the layers of data;
- whether there are different business rules for each data layer; and whether different layers require different transformation algorithms
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.