Is Yunnan a city?

Whan it has a seat----------------A City is a City when it is INCORPORATED....essentially, it then becomes a Buisness It makes money through taxes (property, Sales, etc.) otherwise, an area not...

Both which and what can be used

A city is a city because it was one the the important places in the world.

The plural form of city is cities.

See Village Voyage's directory of city wikis to find out: http://www.villagevoyage.com/wiki/Category:Cities