You have taken off in a small private plane from Brighton City Airport at Shoreham-by-Sea. The plane heads directly due south. About 40 minutes and 177 km later you pass over the coast of France at Ouistreham. Your pilot follows the course of the river Orne. Below you, you spot a white gash amid the pattern of green fields.

The port of Ouistreham, the Orne river and its canal. In the bottom left-hand corner, the modern outskirts of Caen. (c) Google