river in northern Thailand, rising in the northern portion of the Luang Phra Bang Range on the Laotian border and flowing south for 390 miles (627 km). It receives the Yom River near Chum Saeng. Just above Nakhon Sawan the Ping and the Nan rivers combine to form the Chao Phraya River (q.v.). The towns of Nan, Uttaradit, Phichai, and Phitsanulok are on the Nan's banks.