It is bordered by Pyŏktong to the east, Tongchang and Taegwan to the south, Sakchu to the west; to the north, it faces China across the Yalu (Amrok) River.

Changsŏng appears as "Changseong" in South Korea's Revised Romanization and as Changcheng in Chinese records, as during its occupation by Mao Wenlong's forces during the Manchu conquest of China.

Changsŏng's terrain is steep and mountainous, sloping generally downward from the southeast toward the Yalu.

Temperatures are of course much colder in the mountains, with the snows atop Piraebong not melting until late May.

Sericulture is widely practised; other crops include maize, rice, peanuts, gochu peppers, sweet potatoes, and various fruits.