Positional Accuracy Improvement (PAI)

The Ordnance Survey completed its PAI Programme to improve the accuracy of its large scale mapping. PAI was necessary to correct an in-built error in the Mapbase that was inherited on digitisation and was especially significant in rural areas due to the legacy of historical mapping surveying methods. The consequence of PAI is an across the board irregular shift in the position of line and point features on the map.

The repercussion of PAI for RoS is that all registered Titles have to be migrated to the new post PAI version of the map and this may result in up-to-date mapping being unable to be released as background mapping until all registered titles in the area have been updated. In addition, any pending registration affected by the PAI programme will be held until they can be completed and defined on the updated and most accurate version of the Ordnance Survey map. This ensures that applications are completed on the most current and accurate version of the map.

In general this impacts any property which has been surveyed at 1/2500 scale and for RoS, requires that 400,000 (or 25%) of our registered Titles have to be updated to show the corrected position.

This would be an extremely time consuming and resource intensive process and RoS has therefore invested in an electronic conversion system that will help to speed up these updates. Work started on initial counties in January 2009 and the programme is due to be completed by the end of this year.

Completion of the exercise by RoS will result in future Title Plans in rural areas being based on more accurate and current mapping information.

Further information relating to surveying methods employed by OS in completion of their PAI Programme can be obtained through Positional accuracy improvement (PAI) programme from Ordnance Survey

PAI rural revision progress Map