Situated in the northern limit of Japan and the eastern limit of China at that time, Sakhalin Island appeared one of the last regions of the earth not yet explored by western people: not only the region was sparsely populated but also Japan and China have not allowed foreigners to freely travel inside their countries. When Japanese have seen first time western maps of Sakhalin, they were puzzled because it appeared as a peninsula: on the contrary, inhabitants of the region insured that it is an island. So Tokugawa government decided to send Matsuda Denjyuro and Mamiya Rinzo to the island in order to verify the above affirmation. They had also the second mission: after the attack to south Kurils and south Sakhalin by Russians in 1806 and 1807, the government wanted to know how closely Russians were coming and wanted to fix precisely the northern frontier of Japan.
In 1808 they left Hokkaido: Matsuda went to the north along the west cost of Sakhalin while Mamiya along the east cost. Actually Matsuda reached the village of Rakka at the 52th parallel, the closest spot of the island to the continent (only 6km). From that locality, the mouth of Amur River is visible so he was convinced that Sakhalin should be an island and set the boundary marker between Japan and China: from there to the south the most inhabitants are Ainu, under control of Japan, while to the north the most are Nivkh, under control of China. Meanwhile Mamiya Rinzo has been blocked in the eastern cost about the 49th parallel because of the steep topography and decided to pass to the west cost. Then he went to the north following the Matsuda's route and confirmed also that Sakhalin is an island. Afterwards they returned to Shiranushi, a Japanese trading, post located at the southern limit of Sakhalin.
In the next year, the government sent again Mamiya to Sakhalin in order to explore further the northern part of the island. So he left alone Shiranushi, as early as January 1809 and went toward the north. The trip was very harsh because he travelled in winter. He survived by eating roots of grass. Finally, he reached the village of Rakka and went further to the north up to Nanio, village of Nivkh, where Sakhalin separates again completely from the continent. So for him, there was no doubt that Sakhalin is an island.
During his stay in the village, he encountered eyewitness who had seen Russians hunting. He understood that the Russian frontier was near and wanted to explore further. At that moment he learned that the boss of the village was going to Deleng, a Chinese trading post in the continent, in order to bring gifts to the Chinese emperor. So Mamiya decided to go with him. They crossed the strait and went up the Amur River till Deleng, located in actual Russian Maritime Territory. There, Mamiya was welcomed by Chinese officials because he was enable to write! But what he has seen there was unbelievable. Every small people of the south Siberia with different languages was gathering there in order to exchange their goods. They used gestures and cries to let understand their business partners! Here are pictures of that epoch drawn after Mamiya's sketches.