The number of listed Japanese islands is expected to more than double from 6,852 to 14,125 after the government recounted them for the first time in 35 years, according to a source familiar with the matter.
The huge increase resulting from improved accuracy with the digitalization of maps is unlikely to change the size of Japanese territory or territorial waters, the source told Kyodo News on Monday.
The government is expected to release the new figure as early as March, although the number could change as the Geospatial Information Authority of Japan, or GSI, is making final adjustments, the source said.
Moves to reassess the number of listed islands came amid criticism that data was old and the true figure could be vastly different. The new figure could affect entries in educational and other materials.
The government has been using the figure released in 1987 by the Japan Coast Guard. At the time, the coast guard listed by hand islands with a circumference of 100 meters or greater shown on a map of Japan. Islands in lakes or river sandbanks were not included in the total.
In the latest survey, the government counted islands automatically using a computer based on GSI's electronic land map in 2022 and cross-referenced the map with past aerial photographs and other data in order to exclude artificially reclaimed land.
While the computer detected over 100,000 islands, only those with circumferences of 100 meters or greater were selected for the official list.
The total size of national territory is calculated using the same digital map irrespective of listed islands, while the extent of territorial waters will not be affected as remote Japanese islands are subject to a separate survey.
Nagasaki and Kagoshima prefectures in southwestern Japan had 1,479 and 1,256 islands, respectively, while 1,473 were listed in Hokkaido, 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."
Islands in the survey are defined 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."