Do ems physically concentrate in cities, or do they spread out more evenly across the land? Industrial economies today achieve large gains from clumping social and business activities closely together. The more easily that people can quickly travel to visit many different stores, employers, clubs, schools, etc., the more kinds of beneficial interactions become possible. The ability to interact via phones, email, and social media hasn’t reduced this effect; if anything the possibility of additional electronic interaction has usually increased the value of personal visits. Urban economists and other academics have long studied such “agglomeration” effects, and understand them in great detail. We should expect these gains from clumping to continue in an em world ( Morgan 2014 ). Ems want to be near one another, and near supporting tools and utilities, so that they could more easily and quickly interact with more such people and tools. This is especially important for fast ems, who can suffer noticeable communication delays with city scale separations. per person, cities today with twice the population tend to be 10% more economically productive per person. Compared with any given sized city, double-sized cities have per-person 21% more patents, 11% shorter roads, and 9% shorter electrical cables. But these cities also suffer 12% more crime, 17% more AIdS cases, and 34% more traffic congestion costs per person ( Bettencourt et al. 2007 , 2010 ; Schrank et al. 2011 ). Today, one factor increasing the productivity of larger cities is their selectively attracting better workers. But another important factor favoring big city productivity is their giving those better workers more ways to gain from their superior abilities. Optimal city size is in general a tradeoff between these gains and losses. During the farming era most people lived in small communities with populations of roughly 1000. Compared with any given sized village, only about 75% as many people lived in double-sized villages (Nitsch 2005). Thus most farmers lived in the smallest villages, because during the farmer era larger versions suffered higher costs of crime, disease, and transport.
