This Thanka is related with the story about Creation of Kathmandu Valley.
In the Svayambhu-purana, it is related that Manjushree left Mount Pancasirsha to visit the shrine of Svayambhu [presently in Kathmandu], which was on a mountain in the center of Lake Kalihrada. He found the lake filled with aquatic monsters and the temple inaccessible. He therefore 'opened with his sword a valley on the southern side of the lake [presently CHOVAR], the waters of the lake drained through the opening, leaving dry land at the bottom, and this was the Katmandu, the capital city of Nepal. So, he is believed as founder of civilization in Nepal and a 'Wanderer' [mendicant Buddhist priest] who propagated Buddhism into Nepal.