A city is a combination of city and city. The "city" is mainly for defense, and it is an area surrounded by city walls. Densely populated areas are called cities, which generally include residential areas, industrial areas and commercial areas, and have the function of administrative jurisdiction. The administrative jurisdiction of a city may involve a wider scope than itself, including residential areas, streets, hospitals, schools, office buildings, commercial shops, squares, parks and other public facilities.

The basic characteristics of the city:

(1) The concept of city is relative.

Urban and rural areas are two basic forms of human settlements, and their relationship is complementary and inseparable. Without the countryside, the concept of city is meaningless.

(2) Cities are characterized by factor aggregation.

Cities are not only densely populated and densely built areas, but also concentrated places for production, consumption and exchange. The benefit of urban agglomeration is the fundamental driving force for its continuous development, and it is also the essential difference from rural areas. The density of various resources in a city makes it the economic, social and cultural radiation center of a certain geographical space.

(3) Urban development is dynamic and diverse.

In ancient times, it had clear space restrictions. In modern times, it has become a functional area. A series of phenomena such as suburbanization, reverse urbanization and re-urbanization have appeared in western countries. Nowadays, with the development of economic globalization and regional division of labor, great changes have taken place in the traditional functions, society, culture and landscape of cities.

(4) Cities are systematic.

Urban giant system includes economic subsystem, political subsystem, social subsystem, spatial environment subsystem and factor flow subsystem. The relationships among the elements of the urban system are intertwined, overlapping and working together.