The lake region extends from the Pangong t'so (t'so =lake) in Ladak, near the source of the Indus, to the sources of the Salween, the Mekong and the Yangtse.
The loftiest lake so far as observed is Hospa t'so, near the Lingshi plain on the Kashmir frontier; its altitude is given as 17,930 ft.
Travelling by way of Khamba jong directly to Gyantse and Shigatse, he turned eastwards at the latter town, finished the survey of the Yamdok t'so, and crossed the Himalaya into the valley of the Lobratsangpo or Upper Manas river.
From this point the traveller followed a general south-westerly direction around the heads of all the feeders of the upper Dre chu, and thence into the lake region of northern central Tibet, crossing Bonvalot's route south of the Chi-chang t'so and that of Bower a few days farther south.
Near the Namru t'so his farther progress south was arrested and he was compelled to take an easterly course.
General easterly direction past the Mangtza t'so, Horpa t'so, Charol t'so, and around the northern end of the Aru t'so, all important lakes, at an average altitude of about 16,50o ft.
From the Aru t'so the travellers took a south-easterly direction across the great northern plateau or Changtang till they reached the south-east side of the Garing t'so, in about 31° 30 N.
M Grenard after a few days resumed his march, passed east of the Noring t'so, the eastern extremity of Tosu Nor, and thence by the south-east corner of Koko Nor to the town of Sining Fu in Kansuh.
The travellers were compelled to enter Tibet by way of the Lighten t'so in 35° N.
Captain Deasy, of the British army, left Leh on the 27th of May 1896, and crossing the Lanak la, passed by the Mangtza t'so, north of the Horpa t'so, to Teshil kul.
Of unknown country, investigating the lake Ngangon t'so or Ngantse t'so, which had hitherto been only hypothetically mapped, and marched thence over the watershed between this and the Tsangpo.
After a journey of half a year Hedin reached Shigatse; on leaving it he turned north again, intending to explore the large sacred lake Dangra-yumso, west of Ngantse t'so, but when within sight of it he was prevented by Tibetans from approaching it.
In the spring of 1901 the expedition resumed its march eastwards around the Dre chu and the Ja chu (Yalung river), followed up the left bank of the latter and got back to Russian Lelu (Oring t'so) on the 30th of May 1901.