How to read old aerial photographs: how to use Kakomap

Published: August 11, 2026 / About 15 min read

The first trouble when you open an old aerial photograph is not knowing where to look. Land that is black and white and coarse-grained, with road shapes and rows of buildings different from today, does not look like the same place at a glance. A Kakomap location page is arranged from top to bottom as follows: then and now, the eras of photographs for this location, the history of the land, the elevation of this location, access by rail, change seen in the share of built-up area, official land prices (Chika Koji) over time, nearby locations, and articles that feature this location. This article uses Toyosu and Takanawa Gateway City as examples and explains step by step which section to look at and for what.

Go back and forth among three ways of comparing

The very top of the page is the comparison screen that sets then against now. When you open it, at many locations the 1961-69 photograph is selected on the "then" side, and moving the "Then ⇔ now" slider changes how the two photographs overlap. Pressing an era button replaces only the "then" side with the selected era, and the "now" side does not move. Unlike laying old atlases side by side, you can move only time while the composition stays fixed.

The advantage of the overlay is that you can set old and new against each other at the same position on the screen. For features you can follow as lines, such as coastlines and the courses of rivers, the way they shift is easy to see if you move the slider little by little. When you want to check the shapes of buildings or the way lots are cut in detail, switching to "Compare side by side" keeps your eyes from getting lost. When you want to stop and just look, leaving it to "Switch automatically" makes the two photographs alternate. In areas where no photograph is available, an image showing that the area is outside the coverage appears, so that part is not material for judgment.

Just below the screen, a single line appears with the highlight of the era being shown. When you switch eras this line is also replaced, so you know in advance what to look at in that era's photograph. Note that the elevation used for the 3D relief is terrain based on today's surveys, not a reproduction of the terrain at the time of the photograph's era. Look at a 3D view with an old photograph pasted on it as the old appearance laid on top of today's relief.

Look first for what has not changed

The knack of comparing is to look first for what has not changed, not for what has changed. The bends of old highways, the courses of rivers and waterways, the direction of the coastline, the routes of railway tracks, the grounds of temples and shrines, the sites of schools. These hardly move in position even when their surroundings are rewritten in a big way, and they serve as landmarks when you overlay old and new.

Takanawa Gateway City is a typical case. In both the photograph from around 1936-42 and the 1974-78 photograph, the tracks of the rolling stock depot run long and narrow through the center of the frame. Because the landmark of the bundle of tracks has not moved for more than half a century, you can follow what changed beside it and when, using the tracks as the reference. Conversely, at a location like Yumenoshima / Shinkiba, where only the sea surface appears in the older eras, you switch to a way of reading that takes its bearings from landmarks remaining on the land side.

Once you find a landmark, it also helps to decide where on the screen to put it. If you keep the landmark at the center of the screen and stop the slider midway, the two photographs are mixed half and half. If you then move the slider back and forth in small steps without taking your eyes off it, the lines that do not move and the surfaces that do move separate clearly. Rather than trying to survey the whole at once, if you divide the screen into four and check one part at a time, you miss less.

The "Highlights of the photographs" table in the history section is also a clue for this search for landmarks. The era cells of the table can be pressed as they are, and the photograph of the pressed era is loaded into the comparison screen. You can check the points you read in the table directly on the screen without going back up each time. The text of the history of the land and the table of main events are also in this section, so you can match on the spot when and by what a change you noticed in the photograph happened.

Step through the eras one at a time

If you stop after going back and forth between then and now just once, you miss the middle of the change. On reclaimed land and graded land, the stage where only the seawall was built, the stage where lots were cut, and the stage where buildings stood may remain in photographs of separate eras. The basic rule is to step through the eras one at a time.

When you step through them, narrow what you follow to one thing. If you decide to follow only the coastline, or only the tracks, and step through in order from the old side, you can identify between which eras it moved. If you try to see everything at once, your eyes are caught by the differences in image quality between eras and you overlook the change that matters. Photographs of older eras are coarse-grained with strong shadows, while newer eras are in color and finely detailed, so even the same feature looks quite different.

The section on the eras of photographs for this location has a timeline that lines up everything from the old side to now in one row. Pressing a tick puts that era into the comparison screen, so you can step forward without going back from section to section. The eras available differ from location to location: some locations go back as far as around 1936-42, and others have only two photographs, 1961-69 and 1974-78. Because the coverage of each era differs by region, even the same era button can mean a different shooting time depending on the land. The order of the eras and the look of the photographs of each era are summarized in the guide to the eras of aerial photographs.

Read elevation in the east-west / north-south cross-sections

The elevation section first shows the elevation at the center of the location in one line, followed by two cross-section graphs, east-west / north-south. At Toyosu, the value 2.4 m near Toyosu Station appears. But the value of one point alone does not tell you whether the land is on a flat surface or partway up a slope. The cross-section graphs cover about 1 km each way from the center, east-west / north-south, and show the sequence of ground heights as a line. Here you read not the height figures but the shape of the line.

You can check where the two lines cut on the locator below the graphs. On today's aerial photograph, the north-south cross-section is overlaid as a vertical green line and the east-west cross-section as a horizontal blue line. The locator can be enlarged by pressing it, and if you trace over the graph with a finger or the cursor, the traced position is also shown with a mark on the locator side. You can match directly where in the photograph a valley or a cliff that appeared on the graph is.

The vertical direction is greatly stretched. The cross-section heading carries the exaggeration factor, as in "vertical exaggeration ×57", and the factor changes with the width of the screen. This is because a relief of a few meters would not show as a line without stretching, but in exchange the slopes look much steeper than they really are. Do not take the look of a line's slope as it is for the gradient of the land.

The east-west cross-section of Takanawa Gateway City is an easy example. If you go west from the center's 3.4 m, it exceeds 20 m, and if you go east, it falls to around 2 m. If you look only at the one point at the center and read it as flat lowland, you miss that the cliff of a plateau presses close just to the west. Tama New Town (Tama Center) calls for the opposite reading. The center's 88.6 m is on the low side within the cross-section; both east-west and north-south are higher toward the ends, with sections above 100 m. The shape of the line keeps the trace of graded land made by cutting hills and filling valleys.

A section where the line breaks off into a blank is a place where no elevation data is provided. Water surfaces such as the sea and rivers fall into this, so you may read a broken section as water. In the Toyosu cross-sections, part of both the east-west and the north-south line breaks off, and the fact that the reclaimed land is surrounded by water appears as gaps in the line. The heights in the cross-sections are all ground-surface values, so even when a station platform is underground or elevated, the cross-sections plot the height of the ground.

Read the spread of built-up area by its position in the distribution

In the section on change seen in the share of built-up area, how much the share of built-up area within a 500 m radius of the location increased (the spread of built-up area) is given as a figure, from the land use of 1976 and 2021 in the National Land Numerical Information. The point to read is less the value itself than where it stands compared with the other locations on the site. The section has a bar lining up Min / Median / Max, with a mark at the location's position. Words such as "among the largest" or "on the small side" are added as well, so you do not need to remember the figures. Tama New Town Minami-Osawa, where the share of built-up area increased from 7% to 85%, is placed toward the top of the distribution, and Osaki Garden City, where it decreased slightly from 99% to 95%, toward the bottom.

The order of use is also fixed. First see in this section where in the distribution the location is, and then go back to the comparison screen. If a location is toward the top of the distribution, you can search with the guess that somewhere on the screen there should be a place replaced as a whole surface. Conversely, at a location toward the bottom of the distribution, you look for differences that do not move as surfaces, such as changes in the shape of blocks or in how densely buildings are packed. If you cross from the nearby locations section to the neighboring land and compare the same section, the places in that region where change gathered also come into view.

A location with a small value has not necessarily stayed the same. Ukishima / Tonomachi King Skyfront is land whose use was replaced wholesale, from a waterfront factory zone to blocks for research and development, but the change of a screen packed with buildings becoming a screen of other buildings shows up in the figures less than the change of sea becoming land. The way plants appear depending on the shooting season and the difference between black and white and color also mix into the figures. Take the figures as a guide, and in the end the sure way is to compare the photographs themselves.

See the official land prices together with the distance to the standard site

The official land prices over time are the series of the standard site nearest to that location. The address / use of the standard site and the straight-line distance from the location are added, so look at the distance before the shape of the graph. If you place the cursor on a point of the line graph or touch it with a finger, that year and the price per square meter appear. If you open "View as a table", you can read every year in figures.

At Takanawa Gateway City, the series of a residential site in Takanawa 2-chome, about 337 m away, is shown, moving from 1,060,000 yen in 2016 to 1,950,000 yen in the 2026 publication. On the other hand, some locations, like Daiba, have no standard site nearby. The series shown for Daiba belongs to a site for shops / offices / warehouses in Ariake 3-chome, about 1.7 km away, and is not the value of the land of Daiba itself. The farther the distance, the more movements unrelated to that location's circumstances mix in.

The series for Tama New Town (Tama Center) is an example of a shape that falls and then comes back. It is a residential site in Ochiai 1-chome, about 721 m away, which fell from 251,000 yen in 2002 to 210,000 yen in 2012-2013 and is 266,000 yen in the 2026 publication. The photographs alone cannot show that the value of the land was moving like this behind eras in which the look of the photographs hardly changes. The official land price is a value published for each standard site as of January 1 every year, and it does not show the transaction price of individual pieces of land.

From location to location, and outside the map

Toward the bottom of the page, nearby locations and locations with the same origins are lined up with mini maps. If you cross from reclaimed land to reclaimed land, and from a cut hill to a cut hill, you come to see that even in photographs of the same era, the circumstances differ from land to land. The entrance to the articles in which that location appears is in the same area. When you want to browse without deciding where to go, pressing the "See a random location" button at the end of the page takes you to unexpected land. The top page also shows "Today's location", which changes daily.

When the place you want to compare is not available as a location page, open Explore the map. Anywhere in the country, you can move the map and overlay old and today's aerial photographs. There is also a "Go to my location" button, so you can start from the town you live in. In areas where no old photograph is available, the screen says so. You can open it from a location page carrying over the position and era, so you can use it to continue when you wonder about what lies outside the frame of the screen.

Elevation, the change figures, and the official land prices are all guide lines for reading the photographs. The leading role in the reading is the photographs themselves, and the figures are material for checking your reading. The elevations shown are measured values of the ground surface and do not show assumptions for floods or earthquakes. For the disaster assumptions of each piece of land, refer to each local government's published materials through the Hazard Map Portal Site of the Ministry of Land, Infrastructure, Transport and Tourism.

The sources of the photographs and figures are summarized in Sources and data, and the list of places you can compare in Find a location. When you recall the name of a piece of land that interests you, try opening it from there.

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