Valuation of intangible resources natural areas are often defined by intangibles with uncertain market value, such as clean water, fresh air, carbon sequestration and diversity of  life. (SEDO) advises on how to conserve such intangibles and transforms them into tangible revenues, such as by means of Payment for Ecosystem Services (PES) and tourism (e.g. ecotourism), with due consideration of cultural sensitivities.