Editing City (section)

=== Site ===
[[File:Allegheny Monongahela Ohio.jpg|thumb|[[Downtown Pittsburgh]] at the [[confluence]] of the [[Monongahela River|Monongahela]] and [[Allegheny River|Allegheny]] rivers, which flow into the [[Ohio River]]]]
Town siting has varied through history according to natural, technological, economic, and military contexts. Access to water has long been a major factor in city placement and growth, and despite exceptions enabled by the advent of [[rail transport]] in the nineteenth century, through the present most of the world's urban population lives near the coast or on a river.<ref>Marshall (1989), pp. 11–14.</ref>

Urban areas as a rule cannot [[Subsistence agriculture|produce their own food]] and therefore must develop some [[city region|relationship]] with a [[hinterland]] that sustains them.<ref name="Kaplan2004p155">Kaplan et al. (2004), pp. 155–156.</ref> Only in special cases such as [[mining town]]s which play a vital role in long-distance trade, are cities disconnected from the countryside which feeds them.<ref name="Marshall1989p15">Marshall (1989), p. 15. "The mutual interdependence of town and country has one consequence so obvious that it is easily overlooked: at the global scale, cities are generally confined to areas capable of supporting a permanent agricultural population. Moreover, within any area possessing a broadly uniform level of agricultural productivity, there is a rough but definite association between the density of the rural population and the average spacing of cities above any chosen minimum size."</ref> Thus, centrality within a productive region influences siting, as economic forces would, in theory, favor the creation of marketplaces in optimal mutually reachable locations.<ref name="Latham2009p18" />