Later photo: new building footprints marked in red

Surveys · A local authority

Building-change survey from two aerial photos

Every building coded on an older and a recent aerial photo; new, demolished and enlarged buildings flagged in a prioritised findings report for building inspection.

Later photo: new buildings marked in red

Client: A local authority
Field: Surveys
Source: Aerial photos 2020/2022 vs 2023 · oblique imagery

The challenge

Building additions are hard to spot on patrol: they sit in back yards, on rooftops and behind facades. An inspection department needs a list of places worth checking, not another general patrol.

Dense city: buildings in orange and roads in blue over the aerial photo — Dense city: buildings in orange, roads in blue

The solution

We coded every building on two aerial photos from different years and compared them. New buildings, demolished buildings and footprints that grew beyond a threshold agreed with the authority were marked in a change layer. Oblique imagery was used to check added floors, balconies and extensions that cannot be seen from above. Each suspected case got a screenshot, and the findings were compiled in a report by priority.

Earlier aerial photo of a low-rise neighbourhood

The outcome

The inspection department goes out with a sorted list and an image for every finding, and can cross-check it against permit records to focus on additions that were never approved.