Zurich Archives Push to Fix Thousands of Mislabelled Digital Images After Database Audit Flags Widespread Errors

Zurich's two largest public digitisation programmes discovered this week that a combined total of several thousand image records in their shared cataloguing systems carry duplicate or mismatched metadata — a problem that archivists say has quietly compounded over at least three years of merged database workflows. The finding surfaced during a mid-year quality audit completed on 2 July, according to internal review schedules circulated to partner institutions.

The stakes are higher than they might first appear. Both the Zentralbibliothek Zürich on Zähringerplatz and the Stadt Archiv Zürich on Neumarkt feed image records into a centralised heritage portal used by researchers, schools, urban planners and journalists. When a photograph is filed under two conflicting accession numbers — or when a scan of one street scene is tagged with the metadata of a different location — the errors propagate outward into every downstream system that queries the database. Given Zurich's current push to digitise planning documents related to the Wohnungsnot housing shortage, accurate image records have direct administrative consequences.

What the Audit Actually Found

The review covered approximately 140,000 image entries loaded into the shared portal since January 2023. Auditors identified around 4,200 records flagged as probable duplicates, meaning the same physical item had been scanned more than once and filed under separate identifiers without cross-referencing. A smaller subset — roughly 310 records — showed what archivists are calling hard mismatches, where the visual content of an image is provably inconsistent with its attached descriptive tags. That figure is drawn from a preliminary summary document distributed this week to partner institutions including ETH Zürich's gta Archiv on Hönggerberg and the Museum für Gestaltung Zürich in Ausstellungsstrasse.

The root cause appears to be a batch-import script introduced in spring 2023 when the city migrated from an older cataloguing platform. During migration, records lacking a unique persistent identifier were assigned temporary codes that were never systematically resolved. Over three subsequent import cycles, those temporary codes multiplied rather than consolidated. The problem is not unique to Zurich — similar migration-related duplication issues have been documented in heritage digitisation projects in Hamburg and Vienna — but the local scale is significant given that the portal underpins applications including the cantonal school curriculum database and the SBB urban development study commissioned for the Zürich West corridor.

Remediation Timeline and What It Means for Users

Zentralbibliothek staff began manual remediation on 3 July, prioritising the 310 hard-mismatch records first. Archivists expect to clear that subset by 18 July, with the broader duplicate-merge project estimated to run through September. During that window, users accessing the portal may encounter records marked with a yellow advisory flag indicating the entry is under active review. The library is advising researchers to cross-check any image sourced from the portal against its original accession register — physical registers held at the reading room on Zähringerplatz remain unaffected.

For institutions that have already downloaded and republished affected images — including several Zürich Kantonschule course materials uploaded before the audit — the advice is more complicated. Educators have been asked to revalidate any image used to illustrate historical street-level content, particularly photographs tagged to Langstrasse, Wiedikon or the Limmatquai. The gta Archiv on Hönggerberg is separately verifying approximately 600 architectural drawings imported in the same 2023 batch, with results expected before the summer recess ends in mid-August.

The episode adds a technical footnote to a broader debate about how quickly Swiss public institutions should accelerate digitisation under budget pressure. The Kanton Zürich allocated CHF 4.2 million to heritage digitisation in its 2024–2027 planning period, with throughput targets that critics in the archival profession have previously described as optimistic given the staffing levels involved. Whether this week's audit prompts a revision of those targets will likely become clearer when the Stadtrat receives the full remediation report, expected in late September.