You will need a visa if you are not from one of the ECOWAS (Economic Organization of West African States) country. Since January 2014, you can get the visa directly on arrival at the airport.
Every person living on the territory must pay taxes. That is every person regularly living on the country or owning a residence. Those taxes are called "impot sur le revenu".
A visa is required to work in Côte d’Ivoire and is valid for a maximum of three months. An extension is required to stay longer. Natives from an ECOWAS (Economic Community of West African States) member state do not need a visa to work in the country.
The Plateau is downtown Abidjan, being also home to most of the governement buildings and also headquarters to most of the banks and International Companies.
There are also two Industrial areas in Abidjan home to most factories in metropolitan Abidjan. The "Zone Industrielle de Koumassi" (Koumassi's Industrial area) in south abidjan, and the "Zone Industrielle de Yopougon" (Yopougon's Industrial Area) in north abidjan.
Service related businesses are scattered around town besides plateau. Small to Medium enterprises have a tendancy to settle in neighborhoods like Marcory, Koumassi and Deux Plateaux.