Locator map of Tibet (1912–1951), borders about 1945
Own work, derivate of File:Bhutan in Asia.svg
Outline based on folded map in:

Hugh Edward Richardson: Tibet and its History. Oxford University Press, London 1962.Details of baoundary in Kham according to:

Melvyn Goldstein: A History of Modern Tibet, 1913-1951. The Demise of the Lamaist State. University of California Press, Berkeley 1991, ISBN 0-520-07590-0, Map 6.Map taken, without reference, from:

洪滌塵編著: 西藏史地大綱. 正中書局, Nanjing 1936, S. 254 (online).Based in turn on:

Eric Teichman: Travels of a Consular Officer in Eastern Tibet. Together with a History of the Relations Between China, Tibet and India. Cambridge University Press, Cambridge 1922, Map 4 (online).
Don-kun; original: User:TUBS