OS Positional Accuracy Improvement

The Positional Accuracy Improvement corrected errors in the position of map features of large scale OS data by altering their position relative to the National Grid. GIS and CAD users who digitised their own data using OS Land-Line or MasterMap prior to 2001 may see some features which no longer appear correctly positioned relative to the base-map features. See the pages at the Ordnance Survey website for more details.

OS positional accuracy improvement programme