The division of labour among people results in cities. With the division of labour an economic interdependence arises among individuals. People rely on each other for what they need, and it makes sense to be in close proximity to each other. As the division of labour increased throughout history so did the growth of densely populated areas from villages to towns to cities. This past century's technological advancements have transformed cities into a variety of urban landscapes. Terms like metropolis, megalopolis, conurbation, suburb, exurb, and mega-city all associate to agglomerations of interdependent populations brought on by the division of labour.
People began to specialize in their roles in order to work better as a group. People started working together as hunter-gatherers, a description that implies a division of labour. Their success exhausted the resources of the wilderness. A lack of resources motivated a conversion to agricultural stability. Agricultural communities could improve their chances of success if they worked together to address one group's crop failure with another's surplus. The need to communicate and trade arose. According to the hub-and-spoke distribution paradigm an efficient way for a sparsely populated group to get together for communication and trade is at a central node. Villages became the nodes whose markets fulfilled the functions of communication and trade. The villages that serviced their agricultural regions transformed into cities that service the globe. Humanity has continuously subdivided work to address the needs of a growing population, and cities provide the forum to communicate and resolve those needs.
In nature the division of labour brings about a similar urban environment. Social insects have structures that equate to our cities in their nests, hives, and underground colonies. Social insects make up a small fraction of insect species, but are very successful as they represent 80% of insect biomass. Their success can be attributed to their division of labour from drones, to queens, to workers. This division of labour means they are dependant on each other for the survival and success of the entire species. Social insects are known for their tools of communication. Chemical trails and ritual dances communicate the needs of the collective to individuals. When you agitate a centipede or cockroach they don't send an attack signal to their peers. On the other hand, when you disturb a wasp nest or cover the entrance to an ant colony the entire group reacts. Social insects as humans have discovered working as a team brings about a greater chance of success for the whole than if each individual tries to fend for them selves.
The last century has lead to improved transportation infrastructure. This improvement is as influential at dispersing cities as the division of labour is at bringing them together. Suburban sprawl in North America is an example of infrastructure pulling cities apart. The division of labour hasn't lessened, but the building of highways, railroads, and airports has allowed people to live in a less intense urban environment. Economic interdependence among Americans is as strong as ever, but increasingly relies on hyper-efficient distribution and telecommunication networks instead of high population density.
The two factors influencing city growth today are telecommunication advancements and transportation infrastructure. The third world's mega-cities have experienced advancement in telecommunications without the transport infrastructure keeping pace. Cell phones and internet efficiently communicate new needs that are fulfilled by increasingly specialised jobs. This leads to fast growing dense cities as people move for the new opportunities, but lack options in commuting due to poor transportation. North America's advanced telecom and transportation infrastructure offers jobs beyond the metropolitan area in the broader megalopolis. The wider region of opportunities disperses the population to suburbs and exurbs. Europe has various city types reflective of different levels in infrastructure development while the communication infrastructure is somewhat equivalent to North America. Transportation deprived Athens lives in hyper-density, while the distribution infrastructure of the Randstad conurbation allows for less intense urban nodes. Around the world urban intensification and suburban growth are dependent on the state of railway and highway infrastructure. Telecommunication development has been more evenly spread and encourages urban growth across the globe.
Cities are the end result from when people began to work as groups and began to divide labour to increase their chance of success. They continued to specialise throughout history, inadvertently increasing their reliance on each other. As interdependence increased so did the need to live in the close proximity of urban environments. Increased efficiencies in the communication infrastructure allowed for new needs to quickly be relayed and new jobs to fill them. Telecommunications has brought the urban boom of the last century. At the same time transportation improvements have stretched city geographies beyond their traditional definitions. Whether urban, suburban, or exurban our economic interdependence arising from division of labour mandates we gather in some form of urbanity.