The countries of the Gulf of Guinea and of the Atlantic with higher rural densities saw a reversal occur before the Sahelian countries. However, the data at the sub-regional and national level cannot show the important differences that exist within countries and across areas, masking areas where the "traditional" system is still possible because arable land is abundant and/or demand centres (markets) are distant. Farmers' production decisions are based on constraints (land, labour and capital), risks and multiple objectives. Urbanisation and the growth of a non-agricultural based economy are the most powerful transformations (Box 4.2). Yet, it is necessary to identify and conceptualise the important differences in livelihoods and production systems to understand producers' constraints and target policies according to the various realities.