One of my first impressions of Africa was the view from the window of a Nigerian Airways Fokker je t as it cruised west from Kano towards the city of Sokoto. Beneath us, the face of Africa was as human-made a landscape as the suburban streets of London and the green fields of Sussex I had left the day before. The ground was etched out in a dense network of fields, their boundaries marked by lines of low bushes, and their surfaces punctured by spreading trees. Every few miles was the rounded shape of a compact village, its rectangular streets marked by trees again, separating a complex hive of compounds. It lay like a densely-packed island of humanity in an open sea of fields.