How Zurich's Digital Archives Got Buried Under Millions of Duplicate Images — and What's Being Done About It

Zurich's public institutions are sitting on an estimated tens of millions of redundant image files, a problem that has grown quietly for more than a decade and is now costing money, slowing down digital services, and complicating the city's push toward a unified open-data infrastructure. The issue, known in records management circles as duplicate image proliferation, has moved from a back-office nuisance to a structural concern significant enough that Stadt Zürich's Stadtarchiv formally flagged it in internal planning documents circulated in early 2026.

The timing matters. Switzerland's federal government updated its records retention ordinance in 2023, placing new obligations on cantonal and municipal bodies to demonstrate clean, deduplicated digital asset registers by the end of 2027. For Zurich, a city that prides itself on administrative precision, falling behind on that benchmark would carry both reputational and legal weight.

How the Problem Accumulated

The roots go back to roughly 2008, when the city's departments began digitising photographic and planning records at scale. Each department — from the Amt für Städtebau to the Grün Stadt Zürich environmental service — operated its own storage environment, with no shared taxonomy and no automatic deduplication protocol. A single aerial photograph of the Limmatquai district, for instance, might exist in four or five departmental folders under slightly different file names, each version slightly different in compression or crop, which meant standard duplicate-detection software failed to catch them.

ETH Zurich's chair for information architecture studied a sample of municipal image repositories in 2022 and found duplication rates ranging from 23 percent to over 40 percent across different departments, depending on how strictly duplicates were defined. That research, published in the journal Records Management Journal, helped shift the conversation from a technical curiosity to a governance problem. Storage costs alone for Zurich's city administration had risen steadily, though the Stadtarchiv has not published a specific line-item figure for image storage in its public budget documents.

The issue is not unique to Zurich. Basel-Stadt encountered a comparable crisis in 2021 when consolidating its urban planning databases ahead of the Erlenmatt district's third phase of development. Bern's cantonal archive began a dedicated deduplication programme in 2024. What distinguishes Zurich is the sheer scale — the city's Volksschulamt education office alone has been digitising school photography going back to the 1970s as part of the broader Erinnerungsort Zürich heritage initiative — and the political expectation, embedded in the 2022 Smart City Zürich strategy, that all civic data assets will eventually be interoperable and publicly accessible.

The Path Forward

Stadtarchiv Zürich is now coordinating with the central IT provider OIZ (Organisation und Informatik) on a phased deduplication project, with the first audit covering records held at the Rathaus and the Stadthaus on Stadthausquai expected to conclude before the end of 2026. The process involves perceptual hashing — a technique that identifies near-identical images even when file metadata differs — alongside manual review for archival items flagged as historically significant.

The project intersects with a broader Swiss push toward open-data compliance. Under the revised Federal Act on Data Protection, which came into full force in September 2023, personal images — including historical school photographs — require additional handling protocols before any public release, adding a layer of complexity to what might otherwise be a straightforward deduplication exercise.

For residents and researchers who use the Zürich city archive's reading room on Neumarkt, or who access the digital portal maintained by the Zentralbibliothek Zürich on Zähringerplatz, the practical effect of the cleanup should eventually mean faster search results and fewer dead-end duplicate hits when querying the visual record. Institutions expecting to submit image-based evidence to planning hearings at the Amt für Städtebau are also advised to check current file submission guidelines, which were updated in April 2026 to require unique-file declarations with each submission. The 2027 federal compliance deadline leaves Zurich roughly 18 months to prove it has the problem under control.