Detecting unpermitted construction from dated imagery
Unpermitted construction is hard to police because it is small, dispersed and continuous. By the time a structure is reported it is already built, and manually reviewing imagery across a whole jurisdiction is impractical.
Detect the change directly
The signal is specific: pixels that classify as unambiguously built today but were not built some months ago. A land-cover classifier runs on both dates, and the difference — new construction — is read out directly rather than inferred.
A three-stage false-positive filter
Naive differencing drowns in noise, so three filters suppress it: asymmetric strictness (the new date must be strongly artificial while any prior built hint is ignored), spectral confirmation (a real NDBI or brightness rise, not an alignment artefact), and a minimum component size that trims speckle while keeping genuine small buildings.
Running on enhanced 5 m super-resolution imagery, it resolves individual structures — a 10×10 m house is several pixels — across areas up to 100,000 km² on an annual cycle. Planning offices, land registries and tax authorities use it to find unpermitted development and verify declared construction without flying or driving the whole territory.