Kostof’s book outlines this question by exploring the history of urban form and the origins of geometric and organic urban patterns. It examines when and why cities began to emerge and how their layouts have evolved. Kostof defines cities not just as physical structures but as cultural, political, and economic entities. This view breaks the monotony of classifying cities into specific types, showing that cities are complex in their growth and essence, which can be viewed as becoming a process of long term change and not as an event that has a certain time frame.

Kostof outlines some basic characteristics of cities, including:

1. Energized crowding of people:
   This characteristic refers to the concentration of population in urban areas. It’s not just about density, but also about the dynamic interactions that occur when people live in close proximity. This “energized crowding” creates opportunities for social, economic, and cultural exchanges. It fosters innovation, specialization of labor, and the development of complex social structures. The energy of a city comes from these constant interactions, creating a buzz of activity and a sense of vitality that is unique to urban environments.
2. Physical circumscription:
   This refers to the defined boundaries of a city, both natural and artificial. Cities are typically delineated spaces, separated from the surrounding countryside or other urban areas. Historically, this might have been in the form of city walls or natural barriers like rivers or hills. In modern times, it could be administrative boundaries, highways, or green belts. This physical definition gives a city its identity and helps in governance and planning. It also influences how the city grows and interacts with its surroundings.
3. Differentiation of uses:
   Cities are characterized by a diversity of functions and land uses within their boundaries. This includes residential areas, commercial districts, industrial zones, public spaces, and more. The differentiation of uses is a key aspect of urban planning and zoning. It reflects the complex needs of urban populations and the way cities organize space to meet these needs efficiently. This characteristic also highlights the specialization and division of labor that occurs in urban environments, contributing to their economic productivity and social complexity.
4. Engagement with surrounding countryside:
   Cities do not exist in isolation but have a symbiotic relationship with their hinterlands. This engagement includes economic relationships (such as trade and food supply), social connections (like migration patterns), and environmental interactions. The countryside provides resources, food, and often recreation spaces for urban dwellers. In turn, cities offer markets, services, and economic opportunities for rural areas. This interdependence shapes both the city and its surrounding regions, influencing patterns of growth, transportation networks, and economic development.
5. Amalgamation of people and planned structures:
   This characteristic emphasizes that cities are more than just collections of buildings; they are living entities that combine human populations with the built environment. The “planned structures” refer to the intentional design and construction of urban infrastructure, buildings, and public spaces. However, the “amalgamation” suggests that cities are not solely the result of top-down planning, but also emerge from the organic interactions between people and their environment. This fusion of human activity and physical form creates the unique character of each city, reflecting its history, culture, and the aspirations of its inhabitants.