Some books have lengthy lives - a measure perhaps of how much they touch their times.
Peter Schwartz's Art of the Long View is one of them. Armed with the most likely maps, the theory goes, we can test out strategies and decisions against different futures, and know where to look for the signals of change. Schwartz uses a fascinating story from ancient Egypt to illustrate the idea of scenarios. In the time of the Pharoahs, the most important event in Egypt was the annual flooding of the Nile and its rich agricultural basin. Each year, the level of flooding was determined by which of these rivers had received the most rainfall and therefore dominated the downstream flow.