Source: United Nations, World Urbanization Prospects 2018.
The geography of cities underlines a strong propensity to locate along the coastline, a pattern associated with several factors. Many coastal areas, particularly deltas, are alluvial plains prone to agriculture and, therefore, for population concentrations. Coastal access is associated with access to trade networks, which historically played an important role as maritime transportation was the least expensive to trade over long distances. The growth of transoceanic trade from the 16th century allowed for the setting of colonial gateways along the coastline of the Americas, Africa, and Oceania. It incited a rebalancing of the urban balance from the hinterland to the coast, a process that expanded in the 20th century with the surge in international trade and containerization.
Of the 513 cities having a population above 1 million in 2015, 271 (52.8%) were located less than 100 km from a coastline. This accounts for 59.4% of the global urban population. This pattern is representative of a high level of concentration of urban activities.