Demand side management (DSM) and distributed generation (DG) introduce into power systems new dynamics and behaviors which must be taken into account in the planning and operation of the system. This paper presents a model that aims to simulate the spread out effects of DSM actions in a region. This model is suitable designed to represent the territorial or local specificities of each studied area where the DSM actions apply. The model involves a large number of input data. The main question is what should be the optimal level of detail this data has to be collected in terms of spatial resolution so that meaningful results are obtained. The paper presents a method to define the input data which are critical to collect with a higher spatial resolution. Results for a case study in France are presented.