Hardly a week goes by without shocking news of a disaster in a city with implications for its future development and, often, for other cities as well. Think of the recent Grenfell Tower fire in London, raising questions about high-rise living elsewhere in London, but also in the Gulf, in Asia and in North America. Density demands that we build up because there are too many pressures on space in the neighbourhoods where people want to live. Human settlement patterns in the 20th century have favored coastal zones. Meanwhile, floods in Thailand and hurricanes in the United States show how difficult the coast can be to manage sustainably.