How Zurich's Digital Archives Ended Up Full of the Same Image Twice: The Road to Duplicate Replacement

Zurich's civic image archive contains tens of thousands of photographs. A growing share of them are exact or near-exact copies of each other. That is the core finding driving a city-wide cleanup effort launched quietly by the Stadtarchiv Zürich and the communications units of several municipal departments earlier this year — an effort that archivists say has been a long time coming.

The problem did not arrive overnight. It is the product of roughly fifteen years of piecemeal digitisation, accelerated by the Covid-19 pandemic, and compounded by the city's aggressive documentation of its own construction boom. Between 2010 and 2025, Zurich issued permits for thousands of new residential units as the Wohnungsnot crisis pushed planners and politicians to document every sod-turning and façade reveal. Each project generated photographs. Those photographs were uploaded — repeatedly — by different teams using different content management systems that did not speak to one another.

Siloed Systems, Duplicated Files

The structural cause traces back to a digital governance gap. The city's Amt für Städtebau, which oversees urban development planning from its offices near Lindenhügel, operated its own media library. The Tiefbauamt, responsible for roads and infrastructure works along corridors like the Hardbrücke and in the Escher-Wyss district, maintained a separate one. The communications team at the Stadthaus on Stadthausquai used a third. When the city contracted ETH Zürich researchers in 2023 to conduct a preliminary audit of municipal data management practices, the team identified redundant file storage as one of the top five cost inefficiencies across cantonal and city-level institutions — though the full report has not been made public.

Private-sector pressure has added to the urgency. UBS, which absorbed Credit Suisse's Swiss operations after the 2023 emergency merger, spent much of 2024 consolidating digital asset libraries across dozens of legacy business units. That consolidation — widely discussed at Zurich's annual Digital Finance Forum held at the Kongresshaus each autumn — pushed vendors of digital asset management software to sharpen their duplicate-detection tools. Several of those vendors then pitched the same products to the city's IT procurement office.

The housing shortage sharpened the documentation problem further. Neuaffoltern, Leutschenbach and the Hunziker Areal in Oerlikon have all been subject to continuous photographic monitoring as part of transparency obligations attached to subsidised Gemeinnütziger Wohnungsbau schemes. A single construction milestone — say, the topping-out of a new cooperative housing block — might be photographed by the developer, the city's own communications officer, a contracted agency and a journalist with a press pass. Four versions of the same image, shot seconds apart, often end up in the same archive under different filenames.

What a Cleanup Actually Involves

Replacing or retiring duplicate images is more labour-intensive than it sounds. Metadata must be reconciled, rights cleared and canonical versions designated before anything is deleted. The Stadtarchiv, which holds records going back to the city's incorporation in 1893 and is based in the former Steinfels soap factory building in Zurich-West, estimates that a full deduplication of its post-2005 digital holdings could take eighteen months to complete. Smaller departmental libraries may move faster.

Automated tools can flag probable duplicates using perceptual hashing — a technique that matches images based on visual structure rather than filename or pixel-perfect identity. But a human archivist still needs to review flagged pairs, particularly where photographs document legally significant events such as permit approvals or public consultations held under cantonal planning law. Errors in that review process carry real administrative risk.

For residents and journalists who rely on city image databases for planning documents or press materials, the practical advice right now is straightforward: if you downloaded a photograph from a municipal source before March 2026, check whether the canonical version has since been updated or replaced on the relevant department's portal. Several departments have already begun issuing revised image packages for major ongoing projects, including the Rosengartentram infrastructure works. The cleanup is incomplete, but it has begun — and the city's digital housekeeping, long deferred, is finally being treated as infrastructure in its own right.