New survey effectively doubles the number of Japanese islands

The number of listed islands has been revised in response to criticism that the data is outdated and the number may differ significantly. The revised figure can impact entries in books and other materials.

The Japan Coast Guard provided the original count of islands in 1987. The coast guard at the time manually classified all islands in Japan with a circumference of at least 328 feet (100 meters). The sum did not include islands in rivers or lakes or sandbanks.

To remove artificially reclaimed land from the current survey, the government used a computer to automatically count islands based on the electronic land map of 2022 from GSI. It cross-referenced the map with earlier aerial pictures and other data.

Only islands with 328 feet (100 meters) or more circumferences were chosen for the official list, even though the computer spotted nearly 100,000 islands.

The entire area of the national territory is estimated using the same digital map, irrespective of listed islands. However, the territorial waters' extent will not change as remote Japanese islands are submitted to a separate survey.

There were 1,479 and 1,256 islands recorded in the prefectures of Nagasaki and Kagoshima in southwest Japan, respectively, while 1,473 islands were listed in Hokkaido in northern Japan.

The recount came after a ruling Liberal Democratic Party lawmaker told a parliamentary session in December 2021 that "an accurate understanding of the number of islands is an important administrative matter that is related to the national interest."

The survey defines islands in line with the United Nations Convention on the Law of the Sea, which states that an island is a "naturally formed area of land, surrounded by water, which is above water at high tide."