Short answers, pulled from the story.
The United Nations Demographic Yearbook from 2015 notes that population thresholds for urban areas range widely depending on local laws and historical context. Some countries set no official criteria at all, leaving definitions to national censuses that invoke factors like population density, number of dwellings, or economic function.
Most scholars consider the Mesopotamian city of Uruk from the mid-fourth millennium BC to be the first true city. This settlement innovated characteristics that would follow in later civilizations including complex societies flourishing in river valleys across Mesopotamia, India, China, and Egypt during the fourth and third millennium BC.
The Indus Valley Civilization built cities on grids aligned with compass points while China's planned cities were constructed according to sacred principles acting as celestial microcosms. Mohenjo-daro of the Indus Valley civilization existed from about 2600 BC and was one of the largest early cities with a population exceeding 50,000 and a sophisticated sanitation system.
Traditional municipal finance relies on local property tax levied on real estate within city limits supplemented by revenue from leasing owned land or selling assets into the private sector. Cities increasingly resort to municipal bonds essentially functioning as loans with interest and repayment dates when seeking ready cash and use tax increment financing to fund development projects based on future expected tax revenues.
Estimates project eighty-seven megacities will exist by 2025 according to United Nations data from 2012. Megacities defined here as cities with more than 8 million people have proliferated into dozens arising especially in Asia Africa and Latin America driven by globalization processes and economic developments over recent decades.