How an artificial island differs from reclaimed land: photographs of Port Island, Daiba, and others

Published: October 12, 2026 / About 15 min read

The difference between an artificial island and reclaimed land is the water left between it and the shore

Artificial islands and reclaimed land are the same in that both are land made by putting soil into the sea. The dividing line lies in their relationship with the shore. Reclaimed land, built by adding soil from the edge of the coast out toward the sea, spreads while staying continuous with the original land. An artificial island is made by drawing its outline with seawalls offshore, away from the shore, and filling in the inside, so even after it is finished, a channel or sea remains between it and the mainland, and bridges, tunnels, and the tracks of a new transit line carry the traffic back and forth. Port Island and Rokko Island in Kobe and Island City in Fukuoka are all land built offshore as separate islands.

Why, then, were they cut off by water instead of being attached to the shore? By stepping through the aerial photographs from the oldest era, you can check whether the water between the land and the shore remains unfilled to the end, and that is where they part from reclaimed land, where land seeps outward from the shore side.

Seawall lines also appear on reclaimed land, and the clue is the water at the boundary

The order in which seawall lines are drawn on the sea first and the inside is filled in later is not a feature of artificial islands alone. The method of enclosing an area first and then putting in sand and soil is the same for reclaimed land attached to the shore, and white seawall lines also appear in the photographs of Kanazawa Seaside Town, which is compared later. The clue for telling them apart is whether the water between the land and the shore stays unfilled as you step through the eras. On reclaimed land, the water surface turns into land in order starting from the side near the shore, but on an artificial island the channel or sea at the boundary with the mainland remains indefinitely, and traffic depends on a few bridges or tracks, so in the photographs these can be read as thin lines crossing the water.

Kobe's two islands, where lines were drawn on the sea first

Kobe is squeezed between the mountains and the sea, and the City of Kobe looks back in its own publications on how it filled in the sea to make artificial islands and expanded the port, in response to a shortage of land to live on and ever-growing cargo. The procedure of filling in the sea offshore with soil cut from the mountains can be read in the article on places that used to be sea and the Osaka Bay shore article.

The 1945-50 photograph of Port Island is almost entirely water, with only ships waiting offshore scattered across it. If you switch to 1961-69, a single thin white line appears on the water. This line, which bends at the lower left and runs straight to the upper right, comes to almost the same position as the southern shore of the island shown in the 1984-86 photograph. Just by going back and forth between the two photographs, you can read the order in which the outline was drawn on the sea first and the contents followed later.

Rokko Island to the east shows the order even more clearly. The 1974-78 photograph shows a seawall line running horizontally across the middle of the sea, sand-colored soil poking its head above the sea surface, and murky water spreading in a fan shape from there to the south, but the island itself is not there yet. A long, thin east-west band appears in 1979-83, and by 1984-86 the full square shape is complete. At that point, the northern shore and the transit sheds and cargo handling areas at the corners are in operation, while the area from the center to the south remains sand-colored bare ground. The order of the outer edge starting work first looks reasonable when you set it against the shape of an island where ships can berth on any of the four sides.

Island City, where a plan connected to the mainland was changed to an island

The place where the decision whether to attach the land to the shore or set it apart offshore remains clearly on record is Island City in Hakata Bay. The basic plan that the City of Fukuoka drew up for Habataki Park on the island states, in the part that traces the course of the deliberations, that the reclamation plan, which had been connected to the mainland, was changed to the island form in order to protect the natural environment of the eastern part of Hakata Bay, including its sea and coast and the Wajiro tidal flat. This passage is placed alongside the 1989 revision of the port plan for Hakata Port. The major difference from Kobe's two islands is that the reason for making it an island is told not in terms of the port's needs but as a matter of protecting the shore side.

The project plan of the City of Fukuoka and Hakata Port Development also describes the soil for the reclamation. The scheme was to dig a deep shipping channel so that large ships could enter and to fill in the land using the dredged sand and soil that came out of it, and construction began in 1994. This means the work of deepening the port and the work of making the island were paired in the same sea.

There are only two past photographs of this location, from 1961-69 and 1987-90. So the appearance of the island can only be checked by bracketing it before and after. The 1961-69 frame is water all over, except for land in a corner along the top edge. In 1987-90, a straight seawall and mid-rise apartment buildings appear in the lower right corner, showing that land was added in order starting from the water near the shore, but there is not a single structure offshore, where the island later sits. Since both photographs show sea with no island, the photographs can tell you only that the island was built after the 1987-90 photograph.

Wakayama Marina City, where no island appears up to the fourth photograph

At Wakayama Marina City, at the southern end of the City of Wakayama, the difference between an artificial island and reclaimed land can be seen side by side within one frame. There are four past photographs, from 1961-69 to 1984-86, and up to the fourth there is no island anywhere. In 1961-69, everything from the left half of the frame to the lower half is one continuous shallow sea, and the only land is the sandy beach and village at the upper right and the woods of the cape.

The change happens on the opposite shore. In 1974-78, the southern shore of the cape juts out squarely into the sea, white round tanks stand in a cluster, and long buildings line up to their north. This is reclaimed land added from the shore out toward the sea, and no water remains at its boundary with the land. Even if you step on to 1979-83 and 1984-86, the factory grounds only become denser, while the sea offshore of them stays sea.

The island shows itself in the photograph as of 2026. A square outline with sharp corners is set in the water, and on the east side a thin line crosses the channel and connects to the shore on the mainland side, where the buildings and tanks stand. In the same sea, factory land attached to the shore and an island cut off by a channel sit next to each other. The measurement points to the east and west of the island have no elevation values, and the cross-section line breaks off there. This is because both sides fall on the sea and the channel, and the way the numbers are missing also shows that it is an island.

Daiba and Shinkiba, which grew while staying surrounded by water

In the photographs from around 1936-42 and from 1945-50 of Daiba, the area around the location is almost all sea, and several square islands of the Shinagawa Daiba, the source of the place name, float on it; these are gun batteries built on the sea at the end of the Edo period. By 1961-69 the number of islands has decreased, and a thin straight line crosses the water on the south side of the frame. It is a seawall line enclosing the lots first, and if you step on to 1974-78, the inside turns into sand-colored bare ground.

The thing to notice here is that a channel was left between the remaining Daiba islands and the new reclaimed land. Even in the 1974-78 photograph, the small green squares stay edged by water and keep outlines separate from the reclaimed land. In the elevation measurement, against 5.8 m at the center, the southern point is minus 2.7 m and the eastern point minus 2.3 m, negative values. This is because the measurement points fall on the water surface, and the numbers also show that this is land open to the sea on three sides.

At Yumenoshima / Shinkiba, land that was not in the photograph from around 1936-42 floats in an angular shape at the center of the frame in the 1945-50 photograph. It is surrounded by sea whichever way you look, and no road or bridge across appears yet. It is in the 1987-90 photograph that an elevated structure crosses the water at the eastern edge and tracks and roads reach the land. The history of the land at Daiba and Shinkiba is left to the Tokyo Bay shore article.

Heiwajima / Oi Pier, cut by canals

Heiwajima / Oi Pier is a part of the reclaimed land that handles the logistics of Tokyo Port. The Tokyo Port Office of the Ministry of Land, Infrastructure, Transport and Tourism states that the Oi container piers were built during the postwar economic boom to expand the logistics functions of Tokyo Port. In the 1945-50 photograph, there is not a single artificial straight line around the location. In 1961-69, a straight seawall line is drawn into the water, and on its inside, mottled bare ground continues south in a band. In 1974-78, the large roofs of warehouses stand in rows, and a green canal crosses the middle of the frame diagonally.

This canal does not disappear as you step through the eras. In 1987-90 several bridges span it, but the water surface itself is kept, and the outlines of the lots stay cut by water. The numbers also show this: there is no elevation value to the east of the location. That direction falls on the water surface of the canal, and of the four directions, with 4.2 m to the north, 4.1 m to the south, and 7.6 m to the west, only the east is missing. The photographs can tell you only the form: the land was not filled in solidly to connect it, and water was left as a break.

Nanko Port Town, which stays sea for three photographs in a row

Because its old photographs are complete, Nanko Port Town on Osaka Bay is a location where you can clearly see how long it was sea. The three photographs from around 1928, from around 1936-42, and from 1945-50 all show water, with neither land nor blocks.

In the fourth, from 1961-69, the frame changes completely. Seawall lines divide the sea first, and the area inside the edge of a polygon made of straight lines folded over one another is bare ground that still has dark, wet mottling and thin drainage streaks. In 1974-78 it becomes a white flat area with only roads and lots laid out, and warehouses and cargo handling equipment line the quay on the north side, but the center is still vacant land. That vacant land changes to rows of slab-shaped residential buildings in 1979-83. The layout, with residential blocks and cargo handling quays fitting on the same island, closely resembles Kobe's two islands. Port Town-higashi Station on the Nanko Port Town Line is the nearest station to the location.

A comparison with Kanazawa Seaside Town, extended by attaching it to the shore

If you set one piece of reclaimed land extended continuously from the shore beside them, the difference stands out clearly. Kanazawa Seaside Town in Yokohama is land built in front of a shore where the hills come right down close to the sea. In the 1945-50 and 1961-69 photographs, factories and round structures are packed into the narrow low land inside the shore, and the shape of the coastline hardly moves. In 1974-78, the area in front of that shore turns into sand-colored bare ground, and a white seawall line continues south while bending.

The difference from the islands of Kobe and Fukuoka is that the bare ground connects directly to the foot of the hills. There is no channel between the new land and the old land, and in the photographs it looks as if the line of the shore had simply been pushed out to sea. In 1979-83, factories line up to the east and long, thin residential buildings to the west, and a wide band of trunk road runs vertically between them, dividing the two areas. Only the northern measurement point is minus 0.8 m because the end of the cross-section falls on the water's edge, and the numbers show how the edge of the flat surface meets the sea directly.

Are the land price records on the island?

If you look at where the official land price points (Chika Koji) are placed, the relationship between the islands and the mainland comes into view from another angle. This is because there are locations with a point on the island and locations with points only on the mainland side across the water. None of the values are for the location itself; they belong to official price points nearby.

At the three locations with a point on the island, the values of land for offices, warehouses, and housing remain as records of the island itself. The values for Rokko Island and Wakayama Marina City are for land on the opposite shore and cannot be read as values for the islands.

Step through the eras to find the photograph where the island appears

Of the nine locations so far, the only case where primary sources confirmed even the reason for cutting the land off from the shore and making it an island was the one in Fukuoka, where a plan connected to the mainland was changed to the island form. The City of Kobe's publications describe the reason for the reclamation and for making artificial islands, not the reason for choosing the island form. For the islands in Tokyo Bay and Wakayama, only the difference in form left in the photographs can be stated. By stepping through the eras, you can tell whether the water between the land and the shore remains to the end, and that is where they part from reclaimed land, where the line of the shore is pushed out to sea.

On the location page, open the oldest era, step forward to the photograph where an outline or land first appears, and then switch to the photograph as of 2026. For Rokko Island the dividing point is the seawall line of 1974-78, and for Yumenoshima / Shinkiba it is the square island of 1945-50. The expected flooding of low land surrounded by sea cannot be read from the photographs, so it is reassuring to check it in each municipality's published materials gathered on the Hazard Map Portal Site of the Ministry of Land, Infrastructure, Transport and Tourism. You can read where the soil for the reclamation came from in the article on places that used to be sea, and the history of each bay in the Osaka Bay shore and Tokyo Bay shore articles.

The prices in this article are actual examples at each point in time and do not reflect market prices after the article was written.