Zurich Archives Push to Fix a Digital Mess Years in the Making

Thousands of duplicate photographs and scanned documents have been quietly jamming Zurich's shared public image repositories for years. This week, city archivists confirmed they are moving to fix it — and the scale of the problem is larger than most officials had publicly acknowledged.

The Stadt Zürich Stadtarchiv, housed on Neumarkt, completed the first phase of a systematic deduplication audit across its digitised holdings on July 2. The review, conducted in coordination with the Zentralbibliothek Zürich on Zähringerplatz, identified redundant image files running into the tens of thousands across joint cataloguing systems. Staff have been instructed to begin manual verification of flagged entries before automated deletion tools are deployed later in the summer.

Why does this matter now? Swiss memory institutions have spent heavily on digitisation over the past decade, and pressure from the Federal Office of Culture to make collections interoperable with national platforms — specifically the Helveticat and Memoriav networks — has intensified since 2024. Storing and indexing duplicate files wastes server capacity, distorts search results, and inflates metadata counts that funders and researchers rely on. In Zurich's case, the redundancy problem grew in part from successive migration projects that copied rather than consolidated image batches.

What the Audit Found

The Stadtarchiv's internal review covered approximately 1.4 million digitised items catalogued since 2011. Of those, early results suggest around 6 percent contain at least one direct duplicate entry — meaning a single photograph or document scanned and uploaded more than once under different reference numbers. A smaller subset involves near-duplicate images: slightly different scans of the same object, often created when analogue originals were re-photographed during equipment upgrades.

The Zentralbibliothek's situation is different in character. Its joint holdings with the ETH-Bibliothek — the research library of ETH Zürich on Rämistrasse — were migrated onto a shared NEBIS catalogue platform in stages between 2018 and 2022. That migration generated a category of ghost duplicates: metadata records pointing to image files that were correctly consolidated on the back end but never cleaned up in the public-facing search layer. Researchers querying digitised maps or historical photographs have been encountering doubled results for at least three years.

The practical cost is not trivial. Cloud storage and server hosting for municipal digital collections ran to roughly CHF 2.1 million in the 2025 city budget allocation for Stadtarchiv operations, according to publicly available cantonal budget documents. Archivists estimate that eliminating confirmed duplicates could reduce active storage load by eight to twelve percent, though the larger saving is in staff time currently spent fielding researcher complaints about redundant search hits.

Next Steps and What Researchers Should Know

The Stadtarchiv expects to run its first automated deletion pass on verified duplicates in September 2026, following a four-week public comment window that opens on July 14. Researchers who have saved direct permalinks to image records are being advised to download local copies before that date, since some URLs pointing to secondary duplicate entries will be retired rather than redirected.

The Zentralbibliothek and ETH-Bibliothek have announced a joint working group that will meet monthly through the end of the year. Their immediate priority is the NEBIS catalogue layer, where a software patch is expected in August. Users accessing digitised Zurich city maps through the online portal will see the most visible change: a cleaner results page with fewer phantom entries cluttering topographic searches.

For institutions watching from outside Zurich, the audit offers a concrete data point on what years of rapid digitisation without parallel data governance actually looks like in practice. The Stadtarchiv is publishing its methodology on its public website from July 7, which smaller cantonal archives in Graubünden and Aargau have already expressed interest in adapting. Cleaning up the archive, it turns out, is its own kind of preservation work.