Novarly Parcel
How we measure ground movement from space
The measurement
Radar satellites (like ESA's Sentinel-1) pass over every city every few days and bounce microwave pulses off the ground. By comparing the phase of these pulses across hundreds of passes over multiple years — a technique called InSAR (interferometric synthetic aperture radar) — scientists can measure whether any patch of ground is rising or sinking, with millimetre-per-year precision. This is peer-reviewed, widely used science: the same technique monitors dams, mines, and volcanoes worldwide.
Our data
We build on the published, peer-reviewed vertical-land-motion datasets of the Ohenhen/Shirzaei group (Virginia Tech): the Nature Cities 2025 dataset covering the 28 most populous US metros (VT Figshare doi:10.7294/27606942, CC0 public domain), the denser 2025 New York City–Long Island deposit (5.1M points, Zenodo doi:10.5281/zenodo.17644691, CC-BY-4.0), and the US Atlantic-coast dataset spanning every East-Coast state from New Hampshire to Florida (VT Figshare doi:10.7294/19350959, CC0). In total we aggregate over 45 million InSAR measurement points to a ~100 m screening grid of ~9 million cells. Contains modified Copernicus Sentinel-1 data.
Shoreline change (coastal addresses)
For addresses within a mile of a measured shoreline, paid reports include the long-term shoreline change rate from the USGS National Assessment of Shoreline Change (public domain) — tens of thousands of transects whose rates are regressed over a century-plus of mapped and satellite shorelines. We report the nearest transect's rate and its distance; retreat is measured history, not a prediction for any single storm or decade.
The risk bands
- Green — worst measured motion near the address is slower than 3 mm/yr downward.
- Amber — 3–10 mm/yr downward measured within 150 m.
- Red — faster than 10 mm/yr downward measured within 150 m.
- No data — no reliable measurement at that spot (vegetated lots, new construction, water). This is not a sign the ground is stable.
We assess the worst measured cell within 150 m of the address — ground risk is local, and a fast-moving patch nearby matters. We also show how that value compares with every measured location in the metro (the percentile), because "2 mm/yr" means more with context.
Hazard context layers (paid reports)
- Wildfire — USFS Wildfire Hazard Potential (2023, 30 m). We sample the address pixel and a ring ~1 km around it: developed lots read "non-burnable" even where surrounding vegetation rates Very High, and it is the surroundings that carry fire to a home.
- Superfund proximity — nearest NPL-relevant site (final, proposed, deleted, or part-of-NPL) within 5 km, from EPA SEMS. EPA-reported coordinates can be approximate; we say so on the report.
- Dam proximity — nearest high/significant-hazard dam within 15 km from the USACE National Inventory of Dams. Hazard classification describes the consequence of failure, not its likelihood.
- Sea-level exposure — the NOAA tide-gauge trend nearest the address combined with measured local ground motion into one effective relative-rise number.
- Drought (farmland) — US Drought Monitor weekly county history since 2000: the share of the county in severe-or-worse drought now, and how often half the county has been there in 25 years.
United Kingdom engines
- Coastal erosion — Environment Agency NCERM 2024 official projections: cumulative metres of expected recession by 2055 and 2105, with and without maintained defences, for the frontage nearest the postcode. Scotland via NatureScot Dynamic Coast historical change rates.
- Coal-mining legacy — Mining Remediation Authority Development High/Low Risk Areas and statutory consultation areas, queried live per postcode; recorded mine entries (shafts/adits) probed and mapped from the National Coal Mining Database view services. A screening before the official CON29M search, never a replacement for it.
- Flood zones — Environment Agency (England), Natural Resources Wales, and SEPA (Scotland) official flood maps, routed automatically by the postcode's nation.
What a screening is — and is not
A screening tells you whether the ground around an address has been measurably moving. It does not tell you whether a specific building is damaged, whether its foundation is sound, or what will happen in the future. Satellite radar measures reflective surfaces (roofs, pavement) — not every parcel has a measurement, and line-of-sight motion is an approximation of pure vertical motion. Treat any amber or red result as a reason to commission a licensed geotechnical engineer — never as a verdict.
How we check it
Every data source a paid report depends on is asked a hand-verified question every morning, every paid report records which sections came back empty as it is built, and every correction we have made is public: how we check our answers.