First, geographical reason. The distance between the Oki island, the nearest island of Japan from Dokdo, is about 157 kilometers, which is approximately 68km farther than from Korea's Ulleungdo. The Sejong chronicles, the official letter during Joseon dynasty, also mentions that the distance between Dokdo and Ulleungdo is close enough to see Dokdo from the other if the weather is fine.

Even document from Japan support that Dokdo belongs to Korea. In the Japan's Justice in 1946, the Allied Supreme Commander's Memorandum, it excluded Dokdo from their territory, and the Allied Supreme Commander's Memorandum issued in June, 1946, also mentioned that Japanese ships and Japanese citizens are not allowed to assess Dokdo within 12 nautical miles.