How Zurich's Digital Archives Got Buried in Duplicate Images — and What the City Is Doing About It

Zurich's city administration is confronting a problem that built up quietly over more than a decade: tens of thousands of duplicate images clogging the municipal digital archive system, driving up storage costs and slowing workflows across departments from the Stadtarchiv on Neumarkt to the communications offices at the Stadthaus on Stadthausquai. The redundancy problem is now severe enough that a formal replacement and deduplication programme has moved from internal discussion to active procurement.

The scale of the issue reflects how municipal digitisation happened in Zurich — fast, departmentally fragmented, and without a unified image-management standard. Between roughly 2010 and 2022, individual city departments scanned historical documents, photographed public infrastructure, and uploaded press materials independently, each using different software and metadata conventions. The result was a sprawling, siloed system where the same image might exist in three or four formats across separate servers, with no automatic mechanism to flag the overlap.

A Problem Rooted in Rapid, Uncoordinated Digitisation

ETH Zurich's digital preservation researchers flagged the broader Swiss institutional trend in a 2023 working paper, noting that mid-sized European municipal archives routinely carry duplicate rates of between 15 and 40 percent of total stored assets when legacy migration projects are not accompanied by deduplication protocols. Zurich's own internal audit, completed in the first quarter of 2025, placed the city's duplicate rate at the higher end of comparable peer institutions, according to a summary presented to the Gemeinderat's digital infrastructure subcommittee in March 2025.

The financial pressure is real. Enterprise-grade archival storage in Switzerland runs at roughly CHF 0.08 to CHF 0.15 per gigabyte per month for cold storage, and substantially more for actively indexed image databases. A municipal archive carrying hundreds of terabytes of redundant data is not an abstract inefficiency — it translates directly into annual licensing and infrastructure costs that compete with service budgets. Informatik Zürich, the city's internal IT department based on Lintheschergasse, has been tasked with leading the technical response.

The timing also connects to broader pressures on Zurich's housing and urban documentation systems. As the city works through its Wohnungsnot crisis and accelerates planning approvals in districts like Altstetten and Schwamendingen, the planning department relies on geolocalised image records to document existing building stock, infrastructure condition, and neighbourhood surveys. Duplicate or misfiled images in those records create genuine administrative risk — wrong photographs attached to planning dossiers, outdated façade images substituted for current site conditions.

The Path Toward a Coordinated Fix

Informatik Zürich began piloting perceptual hashing tools — software that identifies near-identical images even when file names or metadata differ — in the archive's test environment in late 2024. The pilot covered a subset of images held by the Stadtarchiv and the Tiefbauamt, the civil engineering office, which maintains one of the largest photographic inventories in the municipal system due to its ongoing infrastructure monitoring obligations.

The replacement programme, expected to reach full deployment by mid-2027, will also establish a city-wide Digital Asset Management standard requiring all departments to route new image uploads through a centralised intake portal with automatic duplicate detection at the point of entry. That represents a structural change, not merely a cleanup exercise. Departments accustomed to independent file management will require retraining and, in some cases, workflow redesign.

For residents and businesses interacting with city services, the practical effect will eventually show up in faster processing times for permit applications and public records requests, both of which depend on archivists being able to retrieve precise, verified images efficiently. The Stadtarchiv accepts public research requests through its reading room on Neumarkt, and staff there have noted informally that image retrieval is among the more time-consuming parts of fulfilling complex historical enquiries.

The broader lesson from Zurich's experience is straightforward: digitisation without governance creates its own category of disorder. The city arrived at this point not through neglect exactly, but through speed — and now the slower, more expensive work of remediation is unavoidable.