In general, it is true that "there is no type of specially indispensable natural resource to get a high national income or economic progress ... However, natural wealth may have a beneficial influence on income and economic growth" (HerfindahM970). Peru, by the diversity of its environment, has an extremely rich and diverse natural resource potential. But environmental diversity allows a fragmentation of the territory and determines degrees of unequal spatial accessibility which have grave consequences for the development. These dissimilarities explain the difficulties encountered by those who study the Peruvian reality, and the problems faced by planners and politicians in designing regionalization plans with their different stages. Ί' The division of Peru in three large regions is classic. In fact, when Juan Lopez de Velasco published his Geografia y Descripcion Universal de Ias indias in the XVI century, he proposed the names of "llano", "sierra" and "montaria". These major regions cover areas of different sizes and different sociocultural, economic and political importance. The coast is best developed, but it extends only over 144,000 km2 (11.2% of Peru). The Sierra is a region of fragmented space in the process of slow advancement and unequal development extending over 335,170 km2 (26.1% of Peru). Finally, the jungle or Selva is a region of incipient and slow development which covers over 806,041 km2 (62.7% of the territory). All functional organization of the Peruvian space is tied to some physical frictions which have strongly marked the regional division: The coast forms a N-S oriented corridor, 100 km wide in the north, 40 km in the central zone and almost inexistent in the S. This region is limited by the Pacific Ocean in the W, which by itself forms an opaque space by its difficult communication and also a natural region whose potential is not quite clear yet. According to Pulgar Vidal's classification (1941, 1981), the Coast comprises the Chala and part of the Yunga, up to 1 ,000 m asl. The coastal strip is the part of the Chala which leaves the Yunga as a contact region between the Coast and the Sierra. Some institutions, such as the National Institute of Planning (INP), consider as Coast the altitude between sea-level and 1,000 m while most others include all of the Yunga. However, there exist strong latitudinal differences: the Sierra starts at 500 m in the Department of Piura and rises to 1,000 m in central and S Peru. This fact explains the narrowness of the ecological levels as one moves from S to N. Latitudinal differences permit the identification of three zones: the latitudinal "tropical" region with an area of 892,665 km2 (69.5%) which extends from Ecuador to 12°S; the latitudinal "subtropical" region with an area of 361,210 km2 (28%) from 12°S to 17°S; and the latitudinal "temperate-warm" region with 31,340 km2 (2.5%) from 17°S to the border with Chile (ONERN 1976). Thus, the size of the territory plus its altitudinal and latitudinal subdivisions are the principal reasons for the diversity and environmental variety of Peru.