How Istanbul's Building Stock Ended Up Full of Duplicate Images — and Why It Now Matters

Istanbul's property and land-registry system is carrying a quiet administrative burden that officials are only now beginning to quantify: tens of thousands of building records stored across municipal and central-government databases contain duplicate or mismatched images, the result of overlapping digitisation campaigns run by at least three separate bodies over the past decade. The problem has grown acute enough that the Istanbul Metropolitan Municipality's geographic information department began a structured deduplication review in the spring of 2026, according to municipal planning documents reviewed by The Daily Istanbul.

The timing is not accidental. Three years after the February 2023 Kahramanmaraş earthquakes killed more than 50,000 people across southern Turkey, pressure on every Turkish municipality to complete credible, image-verified building inventories has never been higher. Istanbul, sitting on the North Anatolian Fault, needs accurate visual records to prioritise which of its roughly 1.5 million registered structures require urgent seismic retrofitting. Duplicate imagery distorts that triage — a building can appear twice in a risk database with contradictory condition scores attached to each entry.

Three Campaigns, One Mess

The duplication problem has a traceable origin. Between 2014 and 2024, Istanbul's building stock was photographed under at least three separate initiatives: the municipality's own Deprem Risk Azaltma Projesi (DRAP) street-survey effort, the national Tapu ve Kadastro Genel Müdürlüğü (land registry directorate) parcel-update programme, and a separate Urban Transformation Directorate push focused on the roughly 400 neighbourhoods designated as transformation zones under Law 6306. Each team used different file-naming conventions, different coordinate reference systems, and — critically — no shared deduplication protocol. Images taken of the same façade on Bağcılar's Yıldıztepe Caddesi or along the waterfront redevelopment strip in Zeytinburnu were uploaded independently to each database, assigned separate record IDs, and never reconciled.

Real-estate platforms amplified the problem commercially. When landlords and developers began registering properties on Emlakjet and Sahibinden for short-term tourist rentals — a market that expanded sharply after the lira's prolonged depreciation made Istanbul apartments attractive to foreign visitors paying in euros or dollars — many uploaded the same listing photograph multiple times to game search-ranking algorithms. By 2025, both platforms had issued updated listing guidelines requiring unique images per property, but the legacy records remained. The Istanbul Chamber of Real Estate Agents, which has roughly 12,000 member firms, flagged the issue in a 2024 sector report, noting that duplicate listings were inflating the apparent vacancy rate in districts such as Beyoğlu and Fatih.

What the Deduplication Drive Involves

The municipality's current review is focused on roughly 280,000 building records held within the IBB-GIS portal, the city's main spatial data system accessible via the Harita Istanbul platform. Technical staff are using perceptual-hash matching — a method that compares images based on visual fingerprints rather than file names — to identify pairs or clusters of identical photographs. Early results from the pilot phase, which covered the Esenyurt and Sultangazi districts between March and May 2026, found a duplication rate of approximately 18 percent across the tested records, meaning nearly one in five image entries was a copy of another already in the system.

That figure, if replicated across the full database, would represent a significant data-quality deficit in a city preparing for the next major seismic event. The DRAP programme alone has allocated funds for assessing 50,000 at-risk buildings in the 2024–2026 budget cycle, and engineers working on those assessments rely on pre-visit imagery to plan site visits. A duplicated or misattributed photograph can send a survey team to the wrong address or cause a high-risk structure to be logged as already assessed.

For residents and property owners, the practical advice is straightforward: if you are involved in any urban transformation process — whether applying for retrofit subsidies through DASK, Turkey's compulsory earthquake insurance scheme, or registering a rental property with the Ministry of Culture and Tourism's new short-term accommodation registry — verify that the photograph on your official record actually matches your building. The IBB's Kentsel Dönüşüm Müdürlüğü office in Bahçelievler accepts correction requests in person or through the e-Devlet portal. The deduplication review is expected to reach the historic peninsula districts of Fatih and Eminönü by the end of the third quarter of 2026.