The location of major cities around the world is far from being random. Although cities have historically required an agricultural base for their support, the development of mechanized transport systems underlined three interdependent factors that played a substantial role in the location of cities.
- Many cities provide connectivity to different systems of circulation, a role that has endured throughout history with port cities, but became prevalent with the growth of international trade from the 19th century. A good port site could become an important city distributing materials and goods and favoring the agglomeration of commercial, industrial, and financial activities. The location of the world’s largest container ports is reflective of the connectivity metropolitan areas are required to act as gateways.
- The distribution of resources is also a factor that incites cities to locate in proximity. The necessity to collect, transform, and distribute resources through the clustering of the related activities is a factor of location and urbanization. Resources can be collected from an area or a punctual location. Agricultural land was historically the main location factor. Still, with the industrial revolution, industrial cities emerged at locations in proximity to inputs such as energy and raw materials, which can be seen as a weighting of ponderous inputs for manufacturing.
- Since cities provide goods and services to a population base, the level of accessibility to this base is a location factor. This is often defined as a market area. Central places theory focuses on this aspect in explaining the distribution of cities, including their sizes, over a region.