 The law defines the Po basin as "the territory from which rainwater or snow and glacier melt flows on the surface, gathers in streams of water either directly or via tributaries...".The United Nations Environment Program includes the Alps and Apennines as far as the sources of the tributaries of the Po but excludes Veneto and that portion of Emilia-Romagna south of the lower Po; that is, it includes the region drained by the Po but only the Po and its tributaries.The altitude of the valley through which the Po flows, exclusive of its tributaries, varies from approximately below sea level in the Polesine subregion (the delta around Ferrara) to about at the river's origin in the southern Piedmontese province of Cuneo, also known as the "Provincia granda".