Hazard Risk / Safety Score (out of 100)

Combines flood-inundation-assumption zones, liquefaction susceptibility, landslide-warning zones, and tsunami-inundation assumptions from the National Land Numerical Information, along with landform classification (former river channels, filled land, terraces, etc.) from the Geospatial Information Authority of Japan, all evaluated at a single center point per town/chome against the hazard/landform maps (since only the center point — not the full area — is checked, results may not exactly match reality for large or boundary-straddling towns/chome). Seismic shaking amplification is not currently included in the formula, as we do not yet have reliable town/chome-level data for it.

Safety Score = 100 − (flood risk × 15 + liquefaction risk × 12 + landform risk + landslide risk × 10 + tsunami risk × 15), clamped to 0–100 and rounded to the nearest integer

Flood Risk (0–4)

Within an assumed inundation zone: assumed depth ≥5m = 4, ≥3m = 3, ≥1m = 2, <1m = 1, outside the zone = 0. Where the source data doesn't record a depth for a zone, we assign a flat "2" regardless of actual depth — so a "2" doesn't necessarily mean moderate depth; it often just means "in the zone, depth unknown."

Liquefaction Risk (0–3)

Uses the rank from the National Land Numerical Information's liquefaction susceptibility map as-is (clamped to a max of 3). 0 = not covered by the liquefaction map; higher values indicate ground more prone to liquefaction.

Landslide Risk (0–2)

Checks whether the area falls within a National Land Numerical Information landslide-warning zone (debris flow, steep-slope collapse, or landslide). Special warning zone ("red zone") = 2, warning zone ("yellow zone") = 1, outside a zone = 0.

Tsunami Risk (0–4)

Within an assumed tsunami-inundation zone: assumed depth ≥5m = 4, ≥3m = 3, ≥1m = 2, <1m = 1, outside the zone = 0. As with flood risk, zones lacking a recorded depth are assigned a flat "2."

Landform Risk (0–20)

Based on the Geospatial Information Authority's landform classification (flood-control landform maps, etc.), higher risk values are assigned to landforms sometimes associated with soft ground or flooding (former river channels, back marshes, filled land, reclaimed land, etc.), and lower values to landforms generally considered more stable (terraces, mountains, etc.), up to a max of 20. Areas that cannot be classified are scored 0 (neutral) — this does not mean low risk.

Because we match against the hazard/landform maps using only a single center point per town/chome, large towns/chome or properties near a boundary may see a score that doesn't match the actual address. Landform risk reflects a statistical tendency based on how the land was formed, not an individual ground survey result. For any specific property, always check the municipality's original hazard map at the address level.