Zurich Takes Methodical Approach to Duplicate Image Problem That Has Stalled Archives in Berlin and Amsterdam

Zurich's city archive, the Stadtarchiv at the Rathaus on Limmatquai, has quietly been working through one of the more unglamorous problems in urban record-keeping: tens of thousands of duplicate image files accumulated across decades of scanning campaigns, departmental uploads and legacy database migrations. The scale is not trivial. According to the Stadtarchiv's published digitisation roadmap for 2024–2026, the archive identified more than 60,000 potentially redundant image entries across its photographic and planning document collections — files that consume server space, confuse search results and, in some cases, have caused planning departments to retrieve outdated building permits instead of current ones.

The timing matters. Zurich's wider e-government push, anchored in the cantonal Digital Agenda programme launched in 2023, has accelerated the consolidation of records from separate municipal departments into unified repositories. When you merge systems — say, the Hochbaudepartement's construction imagery with the Stadtentwicklung Zürich urban planning library — duplicates multiply fast. The same photograph of a Kreis 5 Industriequartier facade can exist in three formats, two resolutions and four different folder hierarchies simultaneously. The problem is not unique to Zurich, but how cities respond to it varies considerably.

What Zurich Does Differently

The Stadtarchiv has contracted with Zürich-based software consultancy Abraxas Informatik, which also handles cantonal IT infrastructure for several Swiss cantons, to run hash-based fingerprinting across its JPEG and TIFF collections. The process assigns each image a unique digital signature; files with identical signatures are flagged for human review before deletion. That last step — the human review — is where Zurich diverges from approaches taken in Berlin and Amsterdam, both of which have automated deletion pipelines with no mandatory archivist sign-off for files below a certain resolution threshold.

Berlin's Landesarchiv faced criticism in 2024 after its automated system discarded what turned out to be unique photographic records of Prenzlauer Berg's 1990s reconstruction, mistakenly tagged as duplicates of lower-quality scans. The incident prompted a formal review, published by the Berliner Senatsverwaltung für Kultur in March 2025, which recommended a hybrid human-machine model — essentially what Zurich had already been doing. Amsterdam's Stadsarchief, for its part, runs quarterly audits rather than continuous review, a model archivists there describe as pragmatic but which has left a backlog of roughly 40,000 unresolved duplicate flags as of its most recent public status report in January 2026.

In Zurich, the Präsidialdepartement allocated CHF 380,000 in the 2025 municipal budget cycle specifically for image deduplication and metadata remediation work across the Stadtarchiv and the linked collections of ETH Zurich's Image Archive, which houses over 2.5 million photographs and collaborates with the city on urban heritage documentation. ETH Zurich's archive, based on the Hönggerberg campus, operates its own deduplication layer independently, but shares standards with the city collection under a memorandum of understanding signed in September 2024.

A Problem With Real Consequences

The stakes reach beyond tidy hard drives. Zurich's housing shortage — the Wohnungsnot — has pushed the Hochbaudepartement to accelerate building permit reviews across neighbourhoods like Altstetten and Oerlikon, where densification projects are moving fast. Incorrect or duplicated planning images have, on at least a handful of occasions confirmed by departmental workflow logs, caused minor but time-consuming errors during permit verification. With construction costs in the city running above CHF 4,500 per square metre for residential builds in 2025, delays of even a few days carry financial weight.

Geneva and Basel have both flagged similar issues in their municipal archives, though neither has published a formal remediation timeline. Geneva's Direction des systèmes d'information et de communication confirmed in a 2025 annual report that image deduplication was listed among priority tasks for 2026 but had not yet been resourced. Basel-Stadt's equivalent programme, managed through the Staatsarchiv Basel-Stadt, is understood to be at an early audit stage.

For residents and researchers, the practical takeaway is this: if you submit a request to the Stadtarchiv Zürich for historical images — whether for a heritage application in Wiedikon or academic research — you are less likely than a year ago to receive a folder full of near-identical files. The archive expects its deduplication project to reach completion by the end of the third quarter of 2026, after which it plans to publish an open methodology document that other Swiss municipal archives can adapt.