Source: Adapted from M. Domosh, R.P. Neumann, P.L. Price and T.G. Jordan-Bychkov (2009) The Human Mosaic: A Cultural Approach to Human Geography, 11th Edition, Cranbury NJ: W.H. Freeman.
Historically, two factors impacted the location of cities; their defense and commercial capabilities. Defensive capabilities are more a site issue since they rely on a defensible physical location that does not necessarily provide good access. At the same time, commerce is more a situation issue that expands the opportunities of a site by putting it on a broader framework of commercial relations.
- Defense. An array of sites offer various defensive advantages that can be expanded by the building of fortifications. This mainly refers to cities established before the industrial revolution since defense was a prime consideration. River meander and island sites are good examples of defensible sites with cities with New Orleans and Paris as prime examples. For cities involved in maritime trade, the coastline also offers defensible sites such as a peninsula (or an offshore island), such as Boston and Hong Kong, or a sheltered harbor site such as New York and Rio de Janeiro. The presence of a promontory can further expand the defensive capabilities of any of the above sites. Modern forms of warfare, particularly artillery, rendered many defensive attributes, such as fortifications, irrelevant.
- Commerce. With the industrial revolution, and in several cases, well before, trade relations became important location factors, with accessible sites along river systems particularly suitable. Bridge-point sites are locations where a bridge could more easily be constructed, such as a narrower river segment. For instance, London was the first suitable site along the Thames River where a bridge could be built. A confluence site benefits from the accessibility of two (or more) river systems, such as the case of Pittsburgh and Chongqing. Portage sites are established to link two river systems that otherwise would not be connected such as Chicago (Great Lakes and Mississippi system). High land transportation costs prior to the industrial revolution underlined the importance of the head of navigation sites, which are the furthest convenient locations that could be reached. Montreal and Minneapolis are such examples.
Improvements in engineering capabilities in the later stages of the industrial revolution would make the advantage of rivers for commercial sites of lesser relevance, particularly with the development of rail and highway systems. Still, once a location has been selected and capitalized upon, the city will remain even if the initial location factors are no longer highly relevant. Thus, a large share of the world’s urban agglomerations was set using some of the above location factors.