As part of our ongoing commitment to data quality, Ordnance Survey completed a national positional accuracy improvement (PAI) programme in 2006. This programme was developed to enable us to capture data at 1:2500 scale to a greater absolute accuracy (absolute accuracy is the position of features in relation to the Ordnance Survey National Grid).
The PAI programme has resulted in an improved and more consistent accuracy standard of mapping data for rural areas. It has also future proofed the data for the addition of new building development and other change, as well as providing a better relationship between Ordnance Survey 1:2500 scale map data and customers' own GPS-positioned resources.
Details of the PAI programme
Work started in April 2001 on the two elements to the national programme; one covering rural towns, the other covering the remaining rural areas.
The rural towns completed in December 2004 and the programme for all other 1:2500 scale rural areas completed in March 2006.
The PAI programme has delivered:
- 210 rural towns (approximately 2 500 km2) to an absolute accuracy of ± 0.4 metres root mean square error (RMSE); and
- all other 1:2500 scale rural areas (approximately 155 000 km2) to an overall absolute accuracy of ± 1.1 metres RMSE.
What does it mean for me as a customer of Ordnance Survey products?
In summary and information you may hold in your GIS derived from our legacy product Land-Line or digitised from old paper plots and plans before 2001 will no longer exactly align to current plots or MasterMap Topography layer.
To 'shift' older data from pre PAI co-ordinates to the newer accuracy co-ordinates we have created PAI 'link files'. Go to the PAI link files page to find out more and request the data.
For starter guidence and case study presentation please see the undertaking PAI documents page.