Buying Property in Japan: What Hazard Maps Can—and Cannot—Tell You

Updated: August 21, 2026 · For property screening before purchase, rebuilding, renovation or change of use

“The hazard map shows blue over the house I want to buy. Should I walk away?”

Start with these three actions:

1. Save the exact map result. Record the layer name, source agency, date, scenario, legend and approximate property location.
2. State what you want to do. Living in the existing house, rebuilding, extending it and changing its use can lead to different questions.
3. Ask for the controlling documents. A designation map, local ordinance, approval record or site investigation may matter more than the first portal screenshot.

About Yamaken. I am a Japan-licensed First-Class Architect, qualified building regulation conformity inspector and Real Estate Transaction Specialist. I spent more than ten years in national and local government, including building-control and urban-planning work, and now work in urban-development consulting, residential design and technical writing. Full profile (Japanese).

My rule is simple: never let one map answer a question it was not made to answer.

What the color does—and does not—tell you

Four different kinds of information tend to collapse into one impression when a buyer sees a colored map. I keep them separate:

1. Hazard information: modelled flood depth, inundation duration, storm surge, tsunami, landslide, terrain, liquefaction or past-disaster information.
2. Legal designation: an area formally designated under a statute or ordinance, such as a 災害危険区域 (saigai kiken kuiki, Disaster Risk Area) under Building Standards Act Article 39.
3. Control over your project: a prohibition, permit, notification or design requirement that applies to a particular building, development, earthwork or use.
4. Evidence about the property: boundaries, levels, soil, retaining walls, drainage, access road, building history, approvals and physical condition.

Imagine two plots. Plot A is shaded for modelled flood depth, but the shading itself does not prohibit a house. It may still affect price, insurance, evacuation and design. Plot B is not shaded on that flood layer, but has an old retaining wall, uncertain drainage and missing approval records. The cleaner-looking map result may belong to the harder property.

The answer changes with your plan

If you will live in the existing house

Concentrate first on the building’s floor level, evacuation route, insurance indication, drainage, retaining walls, past damage and whether the seller can supply building confirmation and inspection records. The question is not only whether a hazard is modelled, but how the existing house and your household would cope with it.

If you may rebuild, extend or change use

Add the legally designated area, local ordinance, city-planning controls, development-permission history and any structural or site measures to the file. A house that can continue to be occupied is not automatically a house that can be replaced in the form you expect. Short-term accommodation or another business use may raise still more questions.

How I use Japan’s Hazard Map Portal

Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT) Hazard Map Portal provides two useful starting points:

• 重ねるハザードマップ (Kasaneru Hazard Map, Layered Hazard Map) overlays nationwide information such as river flooding, rainwater inundation, storm surge, tsunami, landslide and terrain characteristics.
• わがまちハザードマップ (Wagamachi Hazard Map, Municipal Hazard Map) links to maps published by municipalities under the relevant laws.

I search the address, check the pin against recognizable parcel features and turn on one layer at a time. I then move from the national portal to the source agency’s latest map. A screenshot without the source, date, scenario and legend is little more than a colored picture.

What an unshaded location means

In a screening note, I would write: “No applicable attention information was confirmed in the public layers reviewed on this date.” I would not write “safe.” The event may exceed the modelled scenario, a river or drainage system may not be covered, the data may be under revision, the address pin may be offset, or another hazard may require a different map. MLIT’s water-hazard disclosure guidance gives the same caution: a property outside the displayed inundation area must not be presented as having no water risk.

What the broker’s water-hazard explanation covers

When an applicable municipal water-hazard map exists under Japan’s Flood Control Act, the real-estate broker’s 重要事項説明 (jūyō jikō setsumei, explanation of important matters) must use the latest available municipal map and indicate the property’s approximate location. MLIT guidance covers river flooding, rainwater inundation and storm surge maps, and recommends showing evacuation shelters.

That explanation is important, but limited. It does not certify flood safety, check every disaster type, measure the floor level, test drainage, confirm insurance terms or decide whether rebuilding is possible. Keep it in the purchase file, then continue the investigation.

When a local rule can restrict building

Building Standards Act Article 39 uses the term 災害危険区域 (saigai kiken kuiki, “Disaster Risk Area” in the official translation database). Under the current Japanese text checked on e-Gov, a local government may designate an area with serious danger from tsunami, high tide, flooding and similar events by ordinance. The ordinance provides the restrictions needed in that area, which may include prohibiting residential construction or imposing other construction conditions.

The practical consequence is local. Ask for both the designation map or notice and the ordinance text that applies to it. A general portal legend is not a substitute. Depending on the ordinance and your project, the deciding issue may be use, floor height, foundations, structural measures, site treatment, rebuilding or extension.

Why yellow, red and fill maps need different follow-up

A 土砂災害警戒区域 (dosha saigai keikai kuiki, landslide disaster warning area, often yellow) primarily supports risk awareness and evacuation systems. A 土砂災害特別警戒区域 (dosha saigai tokubetsu keikai kuiki, landslide disaster special warning area, often red) is a separate designation that can bring restrictions on certain development and structural requirements for buildings with habitable rooms.

Obtain the prefecture’s designation record rather than deciding from the color alone. It should identify the natural phenomenon, the boundary and, for a special warning area, the parameters used for structural review. Also check separate controls such as a prefectural cliff ordinance, a steep-slope failure danger area, a landslide prevention area or a local Disaster Risk Area.

A 大規模盛土造成地マップ (daikibo morido zōseichi map, large-scale fill map) raises a different question: how was the land made? MLIT expressly says that being mapped does not mean the land is immediately dangerous, and the nationwide display is approximately 1:25,000 in accuracy. Look for the original development drawings, fill geometry, drainage, retaining structures, inspections, later alterations and any stability assessment. Liquefaction and earthquake-shaking maps likewise help frame questions; they do not replace parcel-specific ground or structural investigation.

The minimum file I would build before contract

Four questions I would take to city hall

1. Which official map and designation record control this location? Ask for the newest source, reference date and the document used when a line crosses the site.
2. What changes for my proposed action? State whether you will occupy the existing house, rebuild, extend, renovate, change use, alter the land or operate short-term accommodation.
3. Which office decides each issue? Building control, development permission, erosion control, river management and disaster management may hold different records and authority.
4. What remains unverified? Ask which record, survey or investigation the authority cannot supply, and who should check it before contract or design.

How to record the result without a false score

A single risk score looks tidy but hides the distinctions that matter. Record each check separately:

• No applicable attention information confirmed in the public sources reviewed — list the sources, dates and limits.
• A public source confirms a restriction or condition — name the designation, rule, affected action and authority.
• Pre-contract or pre-design consultation recommended — state the unresolved fact and the exact office or professional.
• Cannot be determined from public information alone — name the missing record, survey, investigation or interpretation.

Then connect the findings to contract conditions, price, finance, insurance, evacuation, design cost and the possibility that the intended use cannot proceed as assumed. “Ask the city” becomes useful only when the question, document and responsible office are named.