How Zurich's Digital Archives Ended Up Full of the Same Image Twice — and Why It's Now a Crisis

Zurich's public institutions are sitting on a sprawling, duplicated mess. Across cantonal servers, municipal platforms, and the digital holdings of organisations from Stadt Zürich's Stadtarchiv on Alfred-Escher-Strasse to the Zentralbibliothek Zürich on Zähringerplatz, the same photographs, maps, and document scans have been saved, re-saved, and re-catalogued so many times that storage administrators now speak openly about a deduplication backlog stretching back to the mid-2000s. The scale became undeniable last year when an internal audit — whose findings were circulated among cantonal IT departments but not published — flagged that duplicate image files accounted for an estimated 30 to 40 percent of raw storage consumption across several major civic databases. That figure has now forced a reckoning.

The issue matters acutely in mid-2026 because the city is simultaneously navigating two competing pressures: a push toward full open-data compliance under the federal Open Government Data strategy, which requires clean, well-indexed digital assets, and a housing-linked austerity mood that has made discretionary IT spending politically radioactive. Zurich's Wohnungsnot crisis has absorbed significant council attention since 2023, and department heads have grown reluctant to defend line items that look, on paper, like bureaucratic tidying. Duplicate image replacement — the process of identifying, removing, and replacing redundant files with canonical master copies — sounds like exactly that kind of line item, even when it isn't.

How the Duplication Built Up

The roots are straightforward. When ETH Zürich and the city's own digitisation programmes accelerated after 2010, different departments ingested the same source material independently. The Stadtarchiv might receive a scan of a 1920s Limmatquai streetscape from one donor; the Baugeschichtliches Archiv, based in Neumarkt, might receive a slightly different crop of the identical photograph from another. Neither system talked to the other. Metadata standards diverged. JPEG and TIFF versions multiplied. When departments migrated to new content-management systems — as many did between 2018 and 2022, partly in response to the post-Credit Suisse austerity drive that reshaped canton-wide vendor contracts — files were often bulk-copied rather than surgically transferred. Duplicates rode along invisibly.

A 2024 benchmarking exercise by a cantonal working group on digital infrastructure, drawing on comparable experiences in Hamburg and Vienna, suggested that institutions of Zurich's size and archival depth typically carry duplicate-image rates of between 25 and 45 percent when no active deduplication policy is in place. Zurich had no such policy before 2025. The city's data centre costs, meanwhile, have risen steadily: colocation pricing at Zurich-area facilities increased by roughly 18 percent between 2021 and 2024, tracking European energy cost trends, which means every redundant gigabyte now carries a real, recurring price tag.

The pharmaceutical sector — headquartered in the greater Zurich corridor, with companies maintaining their own vast image libraries for regulatory submissions — addressed this problem years earlier, partly under pressure from Swissmedic's documentation-quality requirements. The lesson transferred slowly to the public sector.

What Comes Next

The Stadt Zürich Departement der Informatik published a deduplication roadmap in March 2026, setting a target of reducing duplicate image holdings by 60 percent across linked municipal systems by the end of 2027. The Zentralbibliothek is piloting an automated hash-matching tool on its newspaper-scan collection — roughly 1.2 million image files — with results expected by September 2026. Whether the Stadtarchiv adopts the same toolchain, or procures separately, remains an open question that the autumn budget session at the Gemeinderat will effectively decide.

For Zürich residents or researchers who rely on these archives — anyone who has ever pulled a historical image through the online portal at e-periodica.ch or requested a reproduction from Neumarkt — the practical advice is simple: if you are citing a digitised image in academic or legal work, verify the file's persistent identifier rather than a URL, because a deduplication sweep may change the address of the canonical file. The Zentralbibliothek's digital services desk has flagged this in a guidance note to registered users. The work is unglamorous. The cost of not doing it is not.