On this map the Philippines can be understood, not as a chain of separate islands, but as the highest regions of a huge oblong plateau surrounded by deep gashes in the earth’s crust. To get from Luzon up to Taiwan by going across the ocean floor you would have to plunge into a deep trench, flanked by parallel mountain ranges, and follow it northwards for about three hundred miles. But south of Luzon, in the region where Avi is proposing to lay a network of inter-island cables, it’s all shallow and flat.