The definitions for urban and rural can be found in the Comparability tab for URBAN. This is what it says for Cameroon:
The 1987 and 2005 samples both define urban and rural areas in the same way. Urban areas are groups of cities, and rural areas are groups of villages. A city is defined as an entity which either has an administrative function (i.e. headquarters of a district), or has a population of at least 5,000 inhabitants and the following facilities: a complete primary school, a developed health center, water supply and electricity facilities, and a daily market. A village is a traditional unit headed by a third class chief, and made up of one or more localities or towns (an inhabited site with boundaries, identified by a name recognized by the people).
Hope this helps!