LONDON — The artist James Bridle remembers the first time he heard of military drones. Back then, some seven years ago, it took intensive online searching to track down an image of one. As reports of drones as weapons of war and instruments of surveillance became more common, he wanted to understand them better. For him, they were an idea without a physical reality.

Mr. Bridle found and downloaded the plans for a type of drone used by the United States Air Force and, using string and chalk, drew a full-size outline of the aircraft on the tarmac of the parking lot behind Bridle’s London studio. Seeing the form sketched out as if the drone were casting a full-scale shadow over an urban setting revealed that this previously unseen combat apparatus had a wingspan about the length of a bus.