Tajikistan, officially Republic of Tajikistan, republic in Central Asia, bordered on the north by Uzbekistan and Kyrgyzstan, on the east by China, on the south by Afghanistan, and on the west by Uzbekistan. It is also known as Tadzhikistan, and was formerly the Tadzhik Soviet Socialist Republic (SSR) of the Union of Soviet Socialist Republics (USSR). Tajikistan contains an ethnically based political subunit, the former Gorno-Badakhshan Autonomous Oblast, also known as the Badakhshoni Kuhi Viloyat, which occupies 44.5 per cent of the republic. Tajikistan is extremely mountainous, and settlement is concentrated in the lowlands. Total area is 143,100 sq km (55,250 sq mi). Dushanbe is the capital and largest city.