For the main part (eastern part of Longyou 隴右, and all other circuits): Denis C. Twitchett (ed.), The Cambridge History of China, Vol. 3, Sui and T'ang China, 589–906, Part I. Cambridge University Press, 1979, ISBN978-0-521-21446-9. Map 11 (p. 403): "T'ang China, 742".
For the western extent of civil administration: Cambridge History. Map 8 (p. 281): "Kao-tsung's protectorates in central Asia".
For the western extent of the empire: Wolfram Eberhard, A history of China, University of California Press, 4th edition, 1977, ISBN978-0-520-03268-2. Map 5 (p. 174): "The T'ang realm (about A.D. 750)". p. 172 of online 3rd edition