Funasugi said the recent discovery of the U.S. map showing the islands as Japan’s follows others made by Britain, France and Germany--all of which describe the islets as Japanese territory.

Funasugi was commissioned by the Japan Institute of International Affairs, a Tokyo-based think tank researching foreign and security issues, in 2018 to seek old maps showing the Takeshima isles.

Scientists have constructed local and nation-wide maps of the radioactive particles that rained down when the Fukushima Daiichi nuclear power plant failed after a massive earthquake and tsunami rocked ...