The location and creation of very few communities have been the result of a preconceived plan; neither did they come into being accidentally. Their existence and location have been due to influences of various kinds. In ancient times, defense against enemies drew people together and led them to place their towns at points of advantage. London was located in a swamp, Paris on an island. Commerce and manufactures have long been factors in creating cities and so have political, social and religious influences. Trade routes have often located cities at points where a break in the method of transportation occurs. This is illustrated by seaports where ships load and unload their cargoes, much of which is transshipped by rail; by cities at the head of navigation on a river and by those at the intersection of important highways and railroads.

A city usually commences at that point which is most convenient for its intercourse with the rest of the world. This point may be deep water alongside of solid ground or other considerations of a physical nature. The fort, as a means of defense, was of course the factor determining the starting-point of some early towns.

Geographical and topographical conditions and lines of transportation affect the growth of a city away from its starting-point. Growth in cities has been described by Mr. Richard M. Hurd in "Principles of City Land Values" as of two kinds, central growth which takes place from the heart and from sub-centers of attraction, and axial growth, which pushes outwardly along highways, street railways, and railroads. Central growth, he says, is due to proximity and axial growth to accessibility.

The influences which cause the city's growth often overlap and are harmonized as they come together. Business stays near the center, residences are forced to the outskirts, and other utilities find their most advantageous locations. Retail shops follow into or near new residential districts. Important stores are located in the places where they are accessible to the greatest number of the people who patronize them; wholesalers desire nearness to their customers (the retailers); manufacturers locate because of transportation or water-power, or some other reason; banks, hotels, theaters and public buildings seek the heart of a city or an important sub-center. All of these influences in a great and growing city affect its structure. They are complex and counteracting and are constantly at work, and they are at all times being acted upon by the topographical features of the land such as bodies of water, hills and valleys.