Istanbul's Building Stock Faces a Reckoning: The Key Decisions Ahead on Duplicate Imagery in Earthquake Risk Mapping

A flaw buried inside Istanbul's earthquake preparedness infrastructure has come into sharper focus this summer: duplicate satellite and aerial images, fed into structural risk models used to classify hundreds of thousands of buildings across the city, are producing unreliable vulnerability scores. The problem is not cosmetic. Those scores inform which buildings get fast-tracked for demolition or reinforcement under Turkey's Urban Transformation Law — and which residents get relocated first.

The stakes could hardly be higher. Istanbul sits on or near the North Anatolian Fault, and the 2023 Kahramanmaraş earthquakes, which killed more than 53,000 people across southern Turkey, made brutally clear what happens when structural assessments are wrong or incomplete. Since then, pressure on the Istanbul Metropolitan Municipality (IBB) and the Ministry of Environment, Urbanisation and Climate Change to accelerate building inspections has intensified at every level of government.

Where the Problem Lives in the Data

The duplicate image issue arises when aerial survey passes overlap — a routine occurrence in dense districts like Fatih, Bağcılar and Gaziosmanpaşa, where the building stock is both old and tightly packed. When the same rooftop or façade appears twice in a training dataset used by machine-learning classification tools, the algorithm over-weights that structure's features. In practice, a crumbling 1970s apartment block in Esenler can end up with a misleadingly clean risk profile, while a recently reinforced building nearby gets flagged incorrectly as high-risk.

The IBB's Urban Transformation Directorate, based in Saraçhane, is understood to be reviewing its imagery pipeline. The directorate has been working with datasets acquired between 2021 and 2024 from Turkey's General Directorate of Geographic Information Systems (TKGM). A formal data-quality audit was listed as a workstream in the city's 2025-2026 Urban Transformation Action Plan, published in late 2024, though no completion date for that specific audit has been publicly announced.

For residents of high-risk districts, the timeline matters enormously. The Turkish government's target under its national urban transformation programme is to bring 1.5 million substandard housing units up to seismic code by the end of 2028. Istanbul accounts for a disproportionate share of that total: the city has an estimated 90,000 buildings classified as requiring urgent intervention, according to figures the Ministry of Environment, Urbanisation and Climate Change cited in its 2024 annual report.

Three Decisions That Will Define the Fix

Planners and technical teams now face at least three pivotal choices. The first is whether to quarantine and re-process all imagery collected before a specific cut-off date — a conservative approach that would delay risk scores for thousands of parcels but produce cleaner data. The alternative is a targeted patch: identify only those survey corridors where overlap exceeded a defined threshold, typically set at 30 percent image redundancy in comparable municipal mapping projects in cities like Barcelona and Seoul, and re-run classification only on flagged zones.

The second decision involves which institution leads the correction. The IBB and the ministry have overlapping mandates in Istanbul's transformation zones, and the Saraçhane directorate does not always share data in real time with Ankara. A coordination protocol signed in 2023 was meant to streamline this, but independent urban policy researchers at Istanbul Technical University's Faculty of Architecture have noted publicly that jurisdictional ambiguity remains a persistent obstacle in multi-agency mapping projects.

Third — and most consequential for ordinary residents — is how the corrected data gets communicated to building owners and tenants in districts like Zeytinburnu and Küçükçekmece, where relocation pressure is already high. Misinformation about risk categories spreads quickly through neighbourhood WhatsApp groups, and a sudden reclassification of a building from moderate to high risk can collapse a family's plans within days.

The IBB's e-Dönüşüm portal, accessible via the municipality's main website, currently lets residents check their building's transformation status by entering a parcel number. Officials have previously indicated the portal would be updated to flag data-quality caveats when scores are under review. Whether that functionality will be activated before the next scheduled imagery update — provisionally planned for the autumn of 2026 — is the immediate question. For tens of thousands of Istanbul families waiting for a definitive answer about their homes, that answer cannot come too soon.