Jerusalem. I sleep on the floor next to Tomer in his tiny apartment. He started life as a war photographer. Now he studies at the Bezalel Academy and today I will give my lecture. I prefer this to a hotel. I only have a vague notion of this city. At night I wander around the Damascus gate. A group of hooded youths come up behind me and I have no idea what might happen. They are curious - me with my iPhone on a tripod - shooting local street vendors. The conversation opens ' What app are you using?'