How Zurich's Digital Archives Ended Up Full of the Same Image Twice — and What the City Is Doing About It

Zurich's cantonal administration is confronting a problem that has quietly compounded for more than a decade: thousands of duplicate images sitting across incompatible public databases, inflating storage costs, confusing open-data users, and undermining the credibility of digitisation projects that cost taxpayers hundreds of millions of francs to build. The issue — known in records management as duplicate image replacement — has moved from a back-office nuisance to a governance concern that administrators at Stadthaus Zurich can no longer defer.

The roots of the problem stretch back to the early 2010s, when individual cantonal departments digitised their own archives independently and on separate timelines. The Bauarchiv, the cantonal statistical office at Hirschengraben, and multiple municipal divisions each built their own image repositories using different metadata standards and file-naming conventions. When the city later attempted to consolidate these systems under unified open-data portals — including the data.stadt-zuerich.ch platform launched incrementally from 2015 onward — the merge processes imported duplicates wholesale. Nobody caught them systematically, because no single office had clear ownership of cross-departmental data hygiene.

Why the Problem Grew Undetected for So Long

Swiss direct democracy plays a role here that outsiders rarely appreciate. Budget referenda and the city's collegiate executive structure mean that large IT consolidation projects require broad political consensus before funding is approved. Proposals to hire dedicated data stewardship staff or procure deduplication software were repeatedly scaled back or split into smaller tranches to stay below cantonal referendum thresholds. The result was piecemeal investment — enough to digitise content, not enough to clean it afterward.

ETH Zurich's Data Science Lab, based on Rämistrasse, has studied public-sector data quality in Swiss cities and found that image duplication rates in municipal archives often exceed fifteen percent of total holdings once systems are federated. That figure, cited in internal research presentations the university has shared with city technology officers, suggests Zurich's problem is structural rather than exceptional. The housing shortage crisis has added indirect pressure: planning departments relying on the Geomatik und Vermessung Zürich geospatial image database have encountered duplicate aerial photographs of the same Altstetten or Schwamendingen parcels filed under different cadastral codes, slowing permit workflows at a moment when the city desperately needs faster approvals.

The financial dimension is concrete. Cloud storage contracts negotiated by the city's IT department — Zentrale Informatik, headquartered near Walchetor — are priced partly on volume. Eliminating confirmed duplicates across the three largest public image repositories could reduce active storage requirements by an estimated eight to twelve terabytes, according to figures that have circulated in budget working sessions. At current enterprise storage rates in Switzerland, that translates to savings in the range of CHF 40,000 to CHF 80,000 annually — modest against the broader IT budget, but politically visible when housing and infrastructure funds are under pressure.

What Comes Next for the City's Digital Records

Zentrale Informatik has been tasked with completing a full deduplication audit across the four largest image databases by the end of Q3 2026. The methodology involves automated hash-matching — comparing digital fingerprints of image files — followed by manual review of near-duplicates flagged by the software. Records marked for removal will go through a 30-day challenge period during which originating departments can contest the deletion, a procedural safeguard added after an earlier 2023 pilot inadvertently removed unique historical photographs of Langstrasse from a cultural heritage collection.

For residents and researchers who rely on the city's open-data portals, the practical change will be improved search result quality and more accurate metadata when querying aerial images, building permits, or infrastructure photography. The Stadtarchiv Zürich, located on Neumarkt, has also announced it will align its own deduplication schedule with the cantonal project rather than running a parallel exercise, which archivists argued would risk conflicting deletion decisions on shared files.

The timeline is tight. With the city's next major IT budget cycle opening in autumn 2026, administrators want clean figures on storage efficiency gains before the funding debate begins. Getting the archives in order before those negotiations start is no longer just a technical task — it is a political one.