Urban system[1]​ or urban hierarchy or of cities are expressions for a concept of urban geography and other social sciences that, using the concepts of system (set of dynamic components and their interrelationships), hierarchy (ordering by levels of importance")) and city (urban population nucleus), can be understood in various ways, depending on the scope of application and the specific perspective:

• - Urban system formed by a group of hierarchical cities ("set of settlements located in a given territory, created and organized by the society that inhabits them, and that maintain relationships with each other... the functional relationships between settlements show different levels of dependence, which allows establishing the urban hierarchy that governs the functioning of the system of cities studied. Thus, a settlement is independent if its main flow is directed to a smaller settlement, and it is subordinate if its main flow is directed to a larger city. size").[2]​.

• - Urban system formed internally within a city. It should not be confused with the geographical concept of urban structure and which, also internally, is applied to the division into parts (morphologically and functionally) of a city. Understood in this second way, these dynamic components are classified into: social groups and the environment, both with mutual and constant interaction.

With the evolution of societies in relation to their environment, urban systems have become more complex, and cities can be called "complex urban systems", where it is possible to disaggregate even more components or analysis variables. The very concept "civilization", which is etymologically identified with that of "city", is defined as "complex society".

Modern urban societies have developed forms of city management and administration (city government). The city government in democratic societies is responsible for implementing and controlling urban management and governance within the system, for which there are certain rules of coexistence (laws or ordinances).

Within the environment component, it is possible to differentiate two large subsystems: the natural territory subsystem, composed of multiple variables (soil, subsoil, atmosphere, water, vegetation and climate); and the subsystem built by man (homes, streets, hospitals, schools, etc.), that is, all those physical components required by society to meet its habitat needs.

• - Urban vitality.