Bird's-eye View Aerial City Landscape Photography

In her book The Economy of Cities, Jane Jacobs claims that city-formation preceded the birth of agriculture. Jacobs does not lend her theory to any strict definition of a city, but her account suggestively contrasts what could only be thought of as primitive city-like activity to the activity occurring in neighboring hunter-gatherer settlements. To argue this view, Jacobs suggests a fictitious scenario where a valued natural resource leads to primitive economic activity - she takes obsidian as an example. The stock of obsidian is controlled and traded with neighboring hunting groups. Hunters who do not control the stock travel great distances to barter what they have, valuing obsidian because it "makes the sharpest tools to be had". This activity brings more people to the center as jobs are created and goods are being traded. Among the goods traded are seeds of all different sorts, stored in unprecedented combinations. In various ways, some accidental, the seeds are sown, and the variation in yields are observed more readily than they would be in the wild. The seeds that yield the most grain are noticed and trading them begins to occur within the city. Owing to this local dealing, the city dwellers find that their grain yields are the best, and for the first time make deliberate and conscious selection. The choices made now become purposeful, and they are made among various strains of already cultivated crosses, and their crosses, mutants and hybrids.
• Causes of establishment
Theorists have suggested many possible reasons for why people would have originally decided to come together to form dense populations. In his book City Economics, Brendan O'Flaherty asserts "Cities could persist—as they have for thousands of years—only if their advantages offset the disadvantages" (O'Flaherty 2005, p. 12). O'Flaherty illustrates two similar attracting advantages known as increasing returns to scale and economies of scale, which are concepts normally associated with firms. Their applications are seen in more basic economic systems as well. Increasing returns to scale occurs when "doubling all inputs more than doubles the output an activity has economies of scale if doubling output less than doubles cost" (O'Flaherty 2005, pp. 572–573). To offer an example of these concepts, O'Flaherty makes use of "one of the oldest reasons why cities were built: military protection" (O'Flaherty 2005, p. 13). In this example, the inputs are anything that would be used for protection (e.g.: a wall) and the output is the area protected and everything of value contained in it. O'Flaherty then asks that we suppose that the area to be protected is square and each hectare inside it has the same value of protection. The advantage is expressed as: (O'Flaherty 2005, p. 13)
(1) O = s2, where O is the output (area protected) and s stands for the length of a side. This equation shows that output is proportional to the square of the length of a side.