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You don't, or at least you might not, and I would agree. Equally you might have walked the beach and know.
Its all down to experience and yet another reason why you and I would argue if you don't know what the terrain is like the chute might be a better option.
We all know its worth taking in different sorts of terrain from the air and comparing them with the actual terrain on the ground just in case. We drive past or walk over different fields and think would we want to land in that - and it gives us a reference. I have a pretty good idea what most of the fields are like used for grazing on the Downs and I have walked across L2K beach many times at low tide.
To the extent that Pace argues I suspect we shouldn't lose sight that many fields do present pretty good landing sites and chances are most forced landings will be pretty successful - at least reading the reports that does seem to be reflected by the evidence.