Zurich Archives Push to Purge Duplicate Images From City's Digital Records This Week

Zurich's municipal digital infrastructure took a concrete step forward this week when Stadt Zürich's archive directorate and ETH Zürich's library services both moved to accelerate long-running duplicate-image-replacement programmes, targeting backlogs that have accumulated across shared urban documentation databases since at least 2021. The push reflects a broader reckoning with digital storage costs and data integrity that has been building across Swiss public institutions for several years.

The timing is not accidental. Switzerland's Federal Archives Act amendments, which came into force in January 2026, tightened requirements for public bodies to maintain deduplicated, retrievable digital records. For Zurich, a city that generates tens of thousands of georeferenced photographs annually — from building permit documentation in Altstetten to infrastructure surveys along the Limmat — the administrative burden of storing multiple near-identical copies of the same image has become both a budgetary and a legal concern.

What Happened This Week

On Tuesday, the Stadtarchiv Zürich on Neumarkt confirmed it was running a full audit of its visual holdings using automated hash-matching software, a process that flags files where pixel-level content is essentially identical but metadata differs — a common byproduct of migrating records across successive content management systems. The audit covers material dating back to digitisation projects from 2003 onwards. Staff are expected to complete the first review phase before the end of July, according to the institution's published project timeline posted on its website.

Separately, ETH Zürich's main library on Rämistrasse announced this week that it had completed the first phase of its own deduplication work across the ETH-Bibliothek image portal, which holds roughly 3.2 million items including historical photographs, architectural drawings, and scientific imagery. The library confirmed in a published notice that approximately 47,000 redundant image records had been flagged for replacement or removal during the first half of 2026 alone. The process involves not simply deleting files but substituting lower-resolution or incomplete duplicates with the highest-quality version identified in the collection — a distinction that matters for researchers and journalists who rely on the archive.

The two institutions are not working in isolation. A working group under the Verband Schweizerischer Archivarinnen und Archivare — the professional body for Swiss archivists — has been coordinating shared methodology since early 2025, aiming to prevent duplication at the point of ingestion rather than treating it as a clean-up problem years later. Zurich, as the largest municipal contributor to that working group, is in effect piloting standards that smaller cantons may eventually adopt.

Why Storage Costs Are Driving Urgency

Cloud storage is not cheap at institutional scale. Swiss public sector procurement data published earlier this year indicated that cantonal and municipal bodies collectively spent over CHF 180 million on digital storage and associated services in 2025 — a figure that working group members have cited publicly as motivation for deduplication across all file types, not just images. Photographs and video account for a disproportionate share of raw storage volume.

For Zurich's residents, the practical stakes are modest but real. The city's online Baugesuchsportal — the planning application portal used by property owners across districts from Höngg to Wiedikon — draws on the same underlying document management infrastructure being audited. Cleaner image records mean faster retrieval times and a lower risk of officials referencing outdated or mislabelled photographs when reviewing permit applications.

Both the Stadtarchiv and ETH-Bibliothek expect their current deduplication phases to wrap up before September, when a new academic intake at ETH and increased autumn planning activity at the city level typically spike demand on the systems. Institutions and researchers who rely on image collections from either body should check published access notices through August, as some subcollections may be temporarily unavailable during active replacement processes. The Stadtarchiv's reading room on Neumarkt remains open for in-person requests throughout.