The Tibet Autonomous Region designated by the PRC is about half the area that is historically and culturally Tibetian. Large areas were detached and placed under the authority of neighboring Chinese provinces, including the Dalai Lama's birthplace.
The total area
designated as '
Tibetan' by the PRC is almost co-extensive with ancient Tibetan claims - effectively extending over all of Qinghai Province, sizeable parts of Western Gansu Province, huge chunks of North and West Sichuan and parts of Northern Yunnan Provinces.
The
main differences between PRC designated areas and historical Tibetan claims lie on the Eastern & South Eastern boundaries and the north of Yunnan province.
There's also a large area on the NW border
not claimed by Tibetans, but designated as part of the TAR but claimed by India as Aksai Chin. India claims it as part of Jammu and Kashmir. PRC also claims most of the Arunachal Pradsesh district of India, which includes Bhutan. Tibet includes most of Bhutan (although
not the Eastern half of AP district which
is claimed as Tibetan by the PRC) and some of Ladakh as part of its 'cultural sphere of influence'.
It's all rather convoluted and my memory may be failing me on some of the details - the whole region is a wonderful but surely a (political) map makers nightmare.
I visited Ladakh years back, it's an awesome place, and called 'Little Tibet' for good reason. There are a couple of additional very small areas just south of there also in dispute between India and China (Tibet).
I'm putting a small string of prayer flags in the back window of the car.
I have a Tibetan flag, It was a gift received on a visit there some years back, I've not put it back up since I last decorated, I shall dig it out.