World cities are defined by the functions they serve, especially their place in the world economy. Some large cities are so large and powerful in their influence that they not only dominate their national economy but are also major cogs in the global or international economy.
Mega cities are defined demographically, that is by population size.
Urban dynamics Cities are constantly changing in their forms and functions. A case study of a country town or suburb illustrating one of the urban dynamics of change listed on page 31. You should take care here to identify those parts of the topic which require a case study approach and those that do not. In this topic there are 2 case studies. So, for example, if your case study of urban dynamics in a large city is Chicago, then you could expand that same case study to cover the first part of the topic on world cities.