Depending on their orientation, different social scientists would
point to different explanations for the existence of cities. A military
historian, for example, might say that, unless populations are concentrated
in cities (perhaps contained within high walls), defense against
attack would be difficult. A sociologist might point out that people
like to interact socially, and that they must be spatially concentrated
in cities in order to do so. In contrast, economic explanations for
the existence of cities focus on jobs and the location of employment.
Economists argue that certain economic forces cause employment
to be concentrated in space. Concentrations of jobs lead to concentrations
of residences as people locate near their worksides. The result
is a city.