Japan's westernmost point has moved further west by about 110 meters, after it was decided to include an ocean rock on official maps.

The Geospatial Information Authority of Japan added the rock to its national base map at a scale of 1 to 25,000. It lies in waters off Yonaguni Island in Okinawa Prefecture. The authority decides the extreme points of the country based on the map.

The rock, known as "Tu-ishi," is about 260 meters to the north-northwest of the island. The authority says it conducted a detailed survey using drones and confirmed that the several-square-meter rock remains above sea level even during the highest tide of the year.

It began showing the revised map on its website this month.

The revision does not change Japan's territorial waters or exclusive economic zone, as the rock has already been shown on some other maps, including nautical charts, labeled as a rock that appears at low tide.

In 1987, however, the authority confirmed that the rock always remains above sea level and showed it on its map at a scale of 1 to 5,000. But that was not reflected on its map at the scale of 1 to 25,000.

The authority says the importance of adding the rock is growing, as people are becoming more interested in territorial issues.