Having reached as far as what is now Ajigasawa at the northern end of Honshū, he was unable to cross over to Ezo due to strict restrictions on travel imposed by the Matsumae Domain, turning back instead to Rikuzen Province. In 1845, at the age of 28, for the first time he crossed the Tsugaru Straits, to Esashi, which he left disguised as a merchant, travelling the length of the island for the next seventh months: he walked, with local Ainu as his guides, along the southern Pacific coast from Hakodate to the tip of the Shiretoko Peninsula, where he erected a marker inscribed , before making his way back again to Hakodate, and thence to Edo. The following year, attaching himself as manservant to , he walked from Esashi along the Sea of Japan coast to Sōya, crossing from there to Karafuto, where they traversed the island and explored the east and west coasts of the southern end of what is now Sakhalin. Crossing back over the Sōya Strait, parting company, he walked the coast of the Sea of Okhotsk to the Shiretoko Peninsula before returning to Sōya by boat, then overland via Ishikari, Chitose, and Yūfutsu back to Esashi, and thence again to Honshū; while in Esashi he met Confucian scholar , the two competing each to compose a hundred poems and carve a hundred seals in one day. Three years later, in 1849, on his third Ezo expedition, he sailed from Hakodate to Kunashiri and Etorofu. He had now covered the whole of the north. In the words of Frederick Starr, these journeys were epoch-making, with results of geographic, literary, and political significance. Again, cartography for those regions practically dates from Matsuura. For this, equipped only with a pocket compass, he relied on his own pacing combined with observation from high points. At the same time, as well as active study of the Ainu language, he was becoming increasingly alive to the plight of the Ainu at the hands of unscrupulous traders and agents of the Matsumae Domain.