Explanation:

• Town: The concept of =town‘ can best be understood with reference to =village‘. Population size is not the only criterion. Functional contrasts between towns and villages may not always be clear cut, but specific functions such as, manufacturing, retail and wholesale trade, and professional services exist in towns.
• City: A city may be regarded as a leading town, which has outstripped its local or regional rivals. Cities are much larger than towns and have a greater number of economic functions.
• Conurbation: The term applies to a large area of urban development that resulted from the merging of originally separate towns or cities. Greater London, Manchester, Chicago and Tokyo are examples.
• Megalopolis or mega cities: It signifies =super- metropolitan‘ region extending, as a union of conurbations. The urban landscape stretching from Boston in the north to south of Washington in U.S.A. is the best-known example of a megalopolis.
• Million city: A city having population of above 1 million.