[6] Located on the banks of the Yellow River, it is a key regional transportation hub, connecting areas further west by rail to the eastern half of the country.

From at least the first millennium BC it was a major link on the ancient Northern Silk Road,[11][12] and also an important historic Yellow River crossing site.

Mixed with different cultural heritages, the area at present-day Gansu province, from the 5th to the 11th century, became a center for Buddhist study.

This highway remained the primary traffic route of northwestern China until the completion of the railway from Lanzhou to Ürümqi, Xinjiang.

Lanzhou's old Donggang Airport, located near the city centre, was the primary entry point for combat aircraft provided to China under the Sino-Soviet Non-Aggression Pact, and along with other targets around Lanzhou, including civilian centers, were heavily bombed by the Imperial Japanese Army Air Force and Navy Air Force.

Instances of major air-battles include an IJAAF raid consisting of 30 BR.20 and Ki-21 bombers against civilian targets in Lanzhou on 20 February 1939; 17th PS, 5th PG commander Capt.

They would be joined by pilots of the Soviet Volunteer Group led by Nikolay Garilov and the 15th PS led by Li Debiao, who would all shoot down five more of the Japanese bombers; the northern Chinese air-raid early-warning net headquarters in Xi'an observed 21 of the original 30 IJAAF bombers returning from Lanzhou.

As the Imperial Japanese forces were preparing for Operation Z against the United States and other allies in Southeast Asia and the Pacific by mid-1941, the IJANF were busy training new aircrews in live combat action across China for the upcoming war in the Pacific; on 22 May 1941, Lt. Gao Youxin of the 21st PS, 4th PG engaged an IJNAF raid on Lanzhou in an I-16 fighter aircraft, while avoiding confrontation against the Zero fighters, he shot down a Mitsubishi G3M bomber north of Lanzhou.

The metropolitan area covers more than 20 square kilometres (7.7 sq mi) of urbanisation along the southern banks of the Yellow River, which flows through from west to east.

Lanzhou is situated on the upper reaches of the Yellow River where it emerges from the mountains and has been a center since early times, being at the southern end of the route leading via the Hexi Corridor across Central Asia.

Lanzhou is situated in the temperate zone and has a semi-arid climate (Köppen BSk) with hot summers and cold and very dry winters.

[18] The city is located in a narrow and curved river valley with surrounding mountains causing it to be hemmed in blocking a free flow of air.

According to the National Environmental Analysis released by Tsinghua University and The Asian Development Bank in January 2013, Lanzhou was among the ten most air-polluted cities in the world.

[21] Air quality reportedly was so poor that at times one could not see Lanshan, the mountain rising up along the south side of the city.

[22] Lanzhou is also the home of many factories, including some involved in petroleum processing, and suffers from large dust storms kicked up from the Gobi Desert, especially in the winter and spring.

[24] According to the 2018 WHO database,[25] of 2700 towns listed, Lanzhou has the 158th highest level of PM 2.5 pollution, with an average of 54 micrograms per cubic meter (twice that of Milan).

The large particle PM10 remains high, at 132 micrograms per cubic meter, in part as a result of sand storms.

[26] In recent years, several specimens of the endangered Chinese giant salamander have been found in and near the Yellow River in Lanzhou.

[27][28] On April 11, 2014, Lanzhou officials advised residents not to drink tap water, because benzene levels were 20 times the national limit of 10 micrograms per liter.

As of the 2020 Chinese census, Lanzhou surpassed 4 million population for the first time, with a total population of 4,359,446 inhabitants and 3,042,863 in the built-up (or metro) area of 1,112.9 square kilometres (429.7 sq mi) made of the 4 central urban districts (Chengguan, Qilihe, Anning and Xigu District).

The strong growth has been attributed to parents seeking better education opportunities for their children, retired migrant workers returning to Gansu, improved services in the city and government policies.

Former England international Paul Gascoigne played four games in both a playing and coaching role for Gansu in 2003,[38][39] scoring two goals,[40][41] before returning to England after falling out with the club,[42][43] as his mental state meant that he had to return to America for treatment against drink and depression.

In addition, Lanzhou produces locomotives and rolling stock for the northwestern railways, as well as machine tools and mining equipment.

[66] The urban railway network, Lanzhou Metro, is planned to consist of six subway lines running 207 km (129 mi).

Lanzhou forms an important link in one of the routes of the Eurasian Land Bridge and also provides rail access to Qinghai, Xinjiang and Tibet further to the west.

[72][73] Regular freight services connect Lanzhou to destinations including Chongqing, Hamburg, Almaty and Kathmandu.

[74] In 2016, Lanzhou was ranked 4th of Chinese cities with the worst rush hour traffic jams;[75] however, by 2017, after completion of an urban ring road, it dropped to 33rd place.

Lanzhou has a noted bus rapid transit system which opened in 2013 and won the city an honorable mention at the 2014 Sustainable Transport Awards.

5The claimed province of Taiwan no longer have any internal division announced by Ministry of Civil Affairs of PRC, due to lack of actual jurisdiction.