Are cheap towns dangerous?
A common first question when looking for a home is whether cheap towns are cheap because they are more exposed to disasters. To test it on Settle Map's data, we split the municipalities into four bands by the share of their area inside the worst-case (L2) flood inundation zone, and took the median residential land price and the median 30-year probability of Shindo 6-lower or above in each band. The sample is the 931 municipalities with at least 4 land price samples.
The result runs against the suspicion. The band with a ratio up to 5.0% (206 municipalities) has a median land price of 36,675 JPY/m², while the band over 70.0% (95 municipalities) has 93,500 JPY/m². Municipalities with a wider flood zone have the higher land prices.
| Flood area ratio | Municipalities | Median land price | Median quake probability |
|---|---|---|---|
| up to 5.0% | 206 | 36,675 JPY/m² | 22.1% |
| over 5.0%, up to 30.0% | 449 | 48,500 JPY/m² | 25.7% |
| over 30.0%, up to 70.0% | 181 | 86,800 JPY/m² | 44.3% |
| over 70.0% | 95 | 93,500 JPY/m² | 57.9% |
How to read this table
The table runs from the municipalities with the smallest flood zone to those with the largest. The land price and earthquake probability in each row are medians of the municipalities in that band. We use the median rather than the mean so that extreme prices, such as those in the 23 wards of Tokyo, do not pull the figure up.
The data alone cannot say why. One geographic reason is that cities and built-up areas gather on the lowland plains that large rivers build downstream. Land is dearer near a city, and lowland means a wider flood zone. It is more natural to read a high land price as a sign of demand than as a sign of safety.
Look at the earthquake column too. The median probability is 22.1% for the band up to 5.0% and 57.9% for the band over 70.0%. Floods and earthquakes are separate hazards: even where the band medians move together, individual towns combine them differently, so the two have to be checked separately.
What the numbers do not tell you
The table aggregates municipalities and shows a correlation only. It does not show that the flood ratio sets the land price, or that land price sets the flood ratio.
Municipalities with few samples are left out, because one plot would move their median. Official land price sites are concentrated in urban areas, so the pattern in depopulated areas is harder to see here.
A town with a small flood ratio can still have its houses clustered along a river. Once you have a shortlist, check the address on the Hazard Map Portal's overlay map.
See the flood area ratio on the map