A main problem of political regionalism in France is the actual definition of regions. M. Charles-Brun set out the factors which should be considered and, though old, his enunciation of principles is still of interest. He began with general matters of climate, geology, relief, orientation, natural products, race, customs, history and language. Next, he pointed out that "homogeneity, which is the fundamental feature of the pays, should not, in so far as the region is concerned, be exclusive of a certain amount of variety". The region should "combine opposed elements". Thirdly, he argued that new tendencies, particularly of an economic character, should be taken into account, since professional organizations will be based on a regional system. Under this head he includes population and commercial relations. Finally, he considers size. The new regions should be large enough, not only in area, but also in resources and population, to withstand the influence of Paris, and they should all be roughly of the same size. This last requirement, he realized, could not be fulfilled with mathematical exactness, since Nature does not permit absolute equality of treatment, but some rough correspondence should be attained so that all regions might be sufficiently strong and vigorous, absorption by the stronger and bigger would be avoided, and an equilibrium would be maintained.
This heterogeneous collection of criteria does not greatly help in providing for specific needs. It has often been pointed out by French regionalists that the definition of new regions does, in fact, involve a dual problem. The region must function as an effective unit of government, so that every part is easily accessible to the centre; and it must be a balanced economic unit, that is, it should possess a common basis of activity and interests. Further, the regional capital should be strong enough in virtue of its history and tradition, and of its large population and modern commercial importance, to withstand the influence of Paris, and should in fact be the principal natural (real) centre for the activities and organization of its region. In other words, the regional capital should function for the region as the national capital functions for the State.
French students of the problem have long been agreed that the extent of the sphere of influence of the dominant cities is of paramount importance in defining such homogeneous human units. The regional capitals are "large cities indispensable to the development of the areas which surround them and throughout which their influence radiates", and around which "new regions are gradually evolving from the ancient provinces, shattering the restricted framework of the administrative Departments".