Short answers, pulled from the story.
A human settlement, or locality, is a place where people live and carry out social, economic, political, and cultural activities. The term covers a broad range of inhabited environments, including hamlets, villages, towns, cities, metropolitan regions, and larger settlement systems. Settlements are created through human activity rather than natural processes and typically involve infrastructure and the modification of surrounding environments.
Permanent human settlements developed during the transition from the Pleistocene to the Holocene, independently in multiple regions between roughly 10,000 and 5,000 years ago. For most of the existence of Homo sapiens, who first appeared approximately 300,000 years ago, people lived in mobile hunter-gatherer groups. By about 5,000 years ago, cities with substantial populations had emerged.
Human settlements are commonly classified as urban, suburban, rural, and temporary. Examples range from villages, towns, and cities to suburbs, exurbs, peri-urban areas, refugee camps, and post-disaster housing. They may also be described by spatial arrangement, including nucleated, linear, dispersed, and isolated patterns.
A settlement hierarchy is a system that ranks and classifies settlements by their size and the range of services they provide. Higher levels contain fewer but larger settlements offering specialized services, while lower levels hold many smaller settlements with basic local services. By size, the hierarchy runs from homestead and hamlet up through village, town, city, conurbation, megacity, megalopolis, and the hypothetical ecumenopolis.
Central place theory, introduced in 1933 by Walter Christaller, explains the spatial distribution of cities and settlements based on their role as providers of goods and services. It rests on the concepts of threshold, the minimum market size needed for a service to be viable, and range, the maximum distance consumers will travel for it. August Losch later expanded the model by incorporating production and administrative functions.
Ekistics is a science of human settlements introduced by Constantinos Doxiadis, with the term derived from the Greek word meaning to settle down. It was intended to encompass all scales of human habitation and is built on a hierarchy of fifteen settlement units, from Anthropos, a single person, up to the ecumenopolis, alongside five common elements: nature, society, shells, networks, and culture.
A megacity is a very large urban agglomeration typically defined by a population threshold of between 5 and 10 million inhabitants, though definitions vary and may also consider density or built-up area. Megacities emerged in large numbers during the rapid urbanization of the late twentieth century, with most located in Asia and other developing regions.