How Zurich's Digital Archives Ended Up Full of Duplicate Images — and What It Took to Get Here

Zurich's city administration is sitting on tens of thousands of duplicate digital images — identical or near-identical photographs stored in parallel across at least four separate departmental servers — the result of more than a decade of uncoordinated digitisation drives that each department ran largely on its own terms. The problem, long acknowledged internally, has now moved to the top of the agenda at the Stadtarchiv Zürich on Neumarkt, which is leading a consolidation effort that officials say will stretch into 2027.

The timing matters. With the broader Swiss public-sector push toward unified e-government platforms accelerating after the federal parliament backed the revised E-ID framework in 2023, cities across the country face pressure to demonstrate that their digital infrastructure is fit for purpose. Duplicate image records are not merely a storage nuisance; they degrade search results in public-facing portals, inflate licensing costs, and create version-control problems when departments pull assets for official publications or planning documents.

How the Duplication Built Up Over Years

The roots of the problem run back to roughly 2011, when individual Zurich departments — among them the Amt für Städtebau, responsible for urban planning records, and the Statistik Stadt Zürich unit on Napfgasse — began digitising their own photographic holdings independently. Each unit chose its own file-naming conventions, metadata schemas, and storage vendors. Nobody was coordinating across departments. When a photograph of, say, a streetscape along Langstrasse was needed by both the planning office and the communications team, each simply scanned or re-exported its own copy rather than drawing from a shared repository.

The practice compounded over successive smartphone-era documentation campaigns. Field staff photographing construction sites around Zürich West, or archivists scanning historical prints at the Zentralbibliothek Zürich on Zähringerplatz, uploaded files to whichever drive their department had provisioned. Cloud migration projects in 2018 and again in 2021 moved those silos intact, duplicates and all, rather than rationalising them. By the time a cross-departmental audit was commissioned in early 2024, preliminary findings pointed to duplication rates in some collections running above 30 percent of total image volume — meaning roughly one in three stored image files was a functional copy of something already held elsewhere in the municipal system.

Storage costs are not trivial at scale. Enterprise cold-storage pricing in Switzerland has hovered around CHF 0.02 to CHF 0.04 per gigabyte per month, depending on contract terms, and high-resolution photographic archives can run into multiple terabytes per department per year. The audit, whose scope covered records back to 2008, was completed and submitted to the Stadtrat in the autumn of 2024.

The Cleanup and What Comes Next

The Stadtarchiv's deduplication programme uses perceptual hashing — a technique that identifies visually similar images even when file names and metadata differ — rather than simple checksum matching. That distinction is significant because many of Zurich's duplicates are not byte-for-byte identical; they are the same photograph exported at different resolutions or with slightly altered crops. Standard duplicate-detection tools would miss them. The archive has been piloting the approach on a subset of approximately 80,000 images from the Amt für Städtebau's post-2008 holdings since January 2026.

The broader municipal rollout is scheduled in phases. The first phase, covering the Stadtarchiv's own collections, is due for completion by December 2026. Departments including Statistik Stadt Zürich and the communications office on Roßgasse are pencilled in for integration during the first half of 2027. The end state is a single asset-management platform — the specifications for which were published for public tender in March 2026 — from which any city department can draw images without creating a local copy.

For residents, the practical payoff will show up in Zurich's public map and image portals, where duplicated entries currently appear in search results and occasionally surface conflicting versions of the same building photograph. Journalists, researchers, and planning consultants who regularly use the city's digital holdings should expect those portals to become meaningfully more reliable once the 2027 consolidation phases complete. In the meantime, anyone ordering archival images through the Stadtarchiv should specify their resolution requirements at the point of request — it remains the surest way to receive the authoritative, most current file rather than a legacy copy.