National Transfer Format
The National Transfer Format (NTF) (or maybe National Transmission Format?) is apparently an entirely different thing from the National Imagery Transmission Format, though the latter has .ntf extensions and is also used in geospatial applications. File-format stuff never stops becoming confusing.
This format was originated by the Association for Geographic Information and was used by the Ordnance Survey in the UK. It is still in use in Northern Ireland. It is a vector format.