See the main public data sources Sumilca references, along with the update scope on both the publisher's side and Sumilca's side.
Sources of the data we use
Freshness SLO: within 90 days of the last check (to keep public data trustworthy)
When a deadline is reached we show it as “deadline reached / auto-rechecking” rather than “overdue,” and queue it for automatic recheck the next business day to resolve any doubt first.
Subject to the NIED J-SHIS terms of use (attribution required; conditions apply to secondary use)
2023-12-01
Download: obtain the J-SHIS ground-related data and save the fetch log
Preprocessing: normalize the indicator ranges and reconcile with regional boundary data
Tiling/aggregation: re-aggregate the mean and quantile values by region
Validation: check the error rate against public statistics and the difference from the previous update
2026-02-21
2026-02-21
2026-02-21
144 days ago since last check / Recheck scheduled（2026-05-22 / Past due — auto re-checking / Auto-recheck: 2026-07-16）
* “Publisher updated” is the update timing on the publishing institution's side; “Fetched / Reflected / Last checked (Sumilca)” are Sumilca's operational timings. Each row states the permanent link to the original data and a license note. The freshness SLO is within 90 days of the last check; past 60 days a recheck is recommended, and at 90 days a recheck is scheduled (when the deadline is reached, auto-rechecking is shown).
What the data means, its limits, and how to read it
For each source we lay out what it shows, where its limits are, and how it should be read. We publish not just the source links but the interpretation rules, so the basis for a decision is easy to check later.
Flood
MLIT Hazard Map Portal Site (assumed flood inundation zones)
What this data means
Baseline data showing which areas could be inundated when a river overflows during heavy rain. It lets you compare how likely an evacuation decision may become around a property's location.
Limits & caveats
It is a maximum-assumed-scale scenario; actual inundation depth and arrival time vary with rainfall conditions and the operation of flood-control facilities.
Update frequency differs by municipality, so even at the same point in time there are old/new gaps between regions.
How to read it
The map's color coding is a ranking of risk; near boundary lines, judge with a margin that allows for error.
Check it not for the property alone but across daily routes including the nearest station, school routes, and nurseries.
Landslide
MLIT Hazard Map Portal Site (landslide hazard alert zones)
What this data means
Alert-zone information for debris flows, steep-slope collapses, and the like. It is used to grasp terrain-derived risk and estimate the difficulty of evacuation during torrential rain.
Limits & caveats
There are gaps in currency before and after a zone is designated, and even unzoned areas are not necessarily zero-risk.
Localized measures such as ground improvement or slope-protection works may not be immediately reflected in the published data.
How to read it
Rather than a binary of inside/outside the zone, check it together with the positional relationship to slopes and valley terrain.
First check whether an evacuation route can be secured at night or during heavy rain.
Liquefaction
NIED J-SHIS Japan Seismic Hazard Information Station (liquefaction risk)
What this data means
A wide-area indicator of how prone the ground is to liquefaction during an earthquake. It helps in comparing reclaimed land and low-lying areas.
Limits & caveats
Because it is an estimate at the mesh level, it does not reflect micro-terrain differences within a site or a building's foundation specifications.
Past ground-improvement history may not be incorporated into the latest data.
How to read it
Look at the continuity with adjacent meshes and judge the risk as an area rather than a point.
Together with hazard information, also check long-term repair costs and insurance conditions at the same time.
Noise
Ministry of the Environment continuous monitoring of road traffic noise (nationwide map)
What this data means
Statistical data for grasping traffic-noise trends along arterial roads and the like. It serves as material for comparing the quietness of the living environment.
Limits & caveats
Because it is based on measurement points, it does not include perceived differences arising from a building's floor level, orientation, or window performance.
Seasonal variation in traffic volume and temporary changes due to construction are hard to capture in annual data.
How to read it
Look at the daytime/nighttime difference and judge whether it fits your living hours.
At a viewing, gauge it firsthand by opening/closing windows and on the balcony side, and cross-check against the statistical values.
Sunlight
GSI digital elevation model (DEM) + National Land Numerical Information (land-use zoning, building use)
What this data means
An indicator that estimates how easily sunlight is obtained from terrain and surrounding land use. It affects the outlook for laundry, room temperature, and electricity consumption.
Limits & caveats
Because the individual shape of buildings and future development of neighboring lots cannot be included in the model, changes in future shadows need to be checked separately.
Differences in solar incidence angle by season and time of day cannot be fully expressed by a single value.
How to read it
Read elevation differences together with the density of surrounding buildings so you do not miss spots that have openings even with a low score.
Confirming the actual daylighting during a viewing around the winter solstice improves the accuracy of your judgment.
Ground
NIED J-SHIS ground amplification factor and surface ground data
What this data means
An indicator for wide-area comparison of ground characteristics related to how easily a site shakes. It is used for a relative assessment of perceived shaking and building-damage probability during an earthquake.
Limits & caveats
It cannot directly evaluate the localized ground of old developed land or a building's intrinsic seismic performance.
Because ground data is averaged, fine differences within a block may be buried.
How to read it
Rather than the hazard alone, judge it in combination with building age, structure, and conformity to seismic standards.
Use it to prioritize among candidate locations, and supplement the final decision with an expert inspection or the statement of important matters.
Disclaimer (notes on sources)
Each dataset is based on information published by public institutions, but map boundaries and update timing vary by municipality. Always check the latest details in the materials from each municipality or the original publisher.
