UKHO checks ENCs in AVCS against the best information that is held, as published on the paper chart. If there is a difference UKHO will try to resolve it with the local authority. Otherwise UKHO may create an 'EPNM' to inform the AIO user.
Where there is no equivalent scale Admiralty paper chart, the UKHO does not have any information to compare to the underlying ENC. In that case the Admiralty Information Overlay shows a ‘No Overlay’ feature to inform the user that assessment cannot be made. The screen will display a polygon with Grey hatched fill to indicate the relevant area.