Agglomeration
Agglomeration of economic activities is the phenomenon that has been observed since humans shifted from migratory life to sedentary life after the spread of farming. Urban agglomerations continue today, and the economy of developed countries is typically dominated by cities. Naturally, agglomeration has been one of the major research topics in urban and regional economics. The formal modeling of agglomeration started in 1970s and grew rapidly thereafter. It first focused on the endogenous city formation; in particular, the formation of the central business district within a city, the presence of which has been treated as exogenous in the classical urban economics. The formation of multiple cities and the agglomeration of more general economic activities as well as their spatial coordination were studied in more recent years. Given the economic integration that took place in different parts of the world in the 1990s and thereafter, today agglomeration has become a common keyword in characterizing not only urban and regional economy, but also international economy.