Ground Stability rates how much a location is sinking due to land subsidence, on a five-step scale from L1 (very low) to L5 (severe), because Bangkok sits on soft marine clay.
We assign each building its district's subsidence level (risk_factors.subsidence_level) from published InSAR and groundwater-monitoring studies. Bangkok sank as fast as ~120mm/year in the 1980s; groundwater regulation cut inner-city rates to near zero, but the eastern soft-clay belt and coastal south keep sinking, which compounds monsoon-flood risk over a 10–20 year horizon. District-level estimate, not a per-building survey.