Area based development is a logical result of the changes in the society and the building environment. Since the early í90 there is experienced with area based development: the physical and functional change of an area-without restriction of geographical boundaries- initiated from the urgency of a social problem or economic opportunity, which took place in a long and complex field of force of different participants, and by which spin-off effects via synergy between different functions and with large scale investments are created. Spin-off effects can be defined as the all-embracing structural effects of the area based development. These effects can be positive as well as negative and are very various. The effects have different dimensions: they can occur inside or outside the plan demarcation, they can be intended or not, direct or indirect. Different spin-off effects of area based development are intended and they can be part of the feasibility study and contribute to the decision making process for large scale development. The whole process of area based development can be divided in four different phases. The spin-off effects should be a part of the feasibility study in the early plan phase. Through the insertion of the spin-off effects in the feasibility study the decision-making will be improved. Insight in the spin-off effect is important because they can enlarge the support for the plan and can guarantee that the aim behind the area based development will be achieved.