Bird's-eye View Aerial City Landscape Photography

According to Vere Gordon Childe, for a settlement to qualify as a city, it must have enough surplus of raw materials to support trade. Bairoch points out that, due to sparse population densities that would have persisted in pre-Neolithic, hunter-gatherer societies, the amount of land that would be required to produce enough food for subsistence and trade for a large population would make it impossible to control the flow of trade. To illustrate this point, Bairoch offers an example: "Western Europe during the pre-Neolithic, where the density must have been less than 0.1 person per square kilometer". Using this population density as a base for calculation, and allotting 10% of food towards surplus for trade and assuming that city dwellers do no farming, he calculates that "in order to maintain a city with a population of 1,000, and without taking the cost of transportation into account, an area of 100,000 square kilometers would have been required. When the cost of transportation is taken into account, the figure rises to 200,000 square kilometers...". Bairoch noted that this is roughly the size of Great Britain.
• Urban primacy
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.