There are many different ways to define a city. It can be called a collection of buildings for an economic purpose or a dense human settlement. It can also be defined as any area where the value of the land may be governed by its distance to something. This something is usually the CBD or Central Business District. This is where many of the residents within the city and suburbs will commute to work. A Metropolitan area is where there is an urbanized area of at least 50,000 people. A micropolitan area contains at least one urbanized area with between 10,000 and 50,000 people. Viewing the city through an economics lens is called the field of Urban Economics. It is becoming very popular and includes many new and interesting economic discussions.
The Basics of the Economics of Cities:
Land, Neighborhoods, and Housing:
O'Sullivan, Arthur. Urban Economics 6th Edition. McGraw-Hill Irwin: 2007. Ch. 1-11, 13-14.