The sheer amount of planning and foresight that went into it seems to have been extraordinary. He viewed a lot of the potential landing beaches himself via a submarine, but a lot of the research was done via maps, postcards and photos that were collected (much had been sent in by members of the...
My grandfather was one of the planners.
He had the unenviable task of surveying all of the potential landing beaches (there were a vast number under consideration) to work out what the average hourly casualty rate would be at each (based on geography, potential defences, tide patterns etc)...