And you had to cover the same section of coastline covered in a 'Popular' at regular intervals, and to obtain full coverage of a section of coastline that had high interest, it had to be covered at low tide (potentially exposing any obstructions or shoals), high tide and mid-tide. The coverage had to be performed at a certain distance from the coastline, at a certain height and at a certain speed to ensure the proper coverage was obtained as well as the required overlap between each photo frame to ensure continuous linear coverage of the section of coast being photographed.