Zurich's Duplicate Image Problem: What Happens Next and the Key Decisions Ahead

Zurich's municipal data managers are confronting a problem that has quietly ballooned across city departments: tens of thousands of duplicate digital images stored across overlapping public systems, from the Stadtarchiv on Neumarkt to the property cadastre managed by the Amt für Raumentwicklung. The redundancy has reached a scale that is straining storage budgets and complicating the city's broader push toward leaner, more transparent e-government services.

The timing is not incidental. Switzerland's revised Data Protection Act, which came into full force in September 2023, obliges public bodies to maintain cleaner, more auditable data holdings. For a city that has also committed to a net-zero carbon target by 2040, the energy cost of running duplicate file servers at the Rechenzentrum in Altstetten is no longer a trivial line item. Administrators who once tolerated sloppy archiving practices now face both legal and climate-related pressure to clean house.

Where the Backlog Sits — and Who Owns It

The core difficulty is jurisdictional. The Stadtarchiv, which catalogues historical photographic collections running back to the early twentieth century, operates under different governance rules than the Geomatik + Vermessung Zürich office, which maintains aerial survey imagery and building documentation. Neither unit has a unified deduplication protocol. Staff at both sites have been working from separate vendor contracts, meaning two sets of software tools scan the same underlying image files without speaking to each other.

ETH Zurich's Chair of Information Science has been in informal contact with city officials about piloting an automated image-fingerprinting solution — a hashing approach that identifies pixel-level duplicates regardless of file name or metadata — but no formal mandate has been signed. That decision is now before the city's Informatik-Kommission, which is expected to meet before the August recess. A pilot scope covering the Stadtarchiv's pre-1950 photographic holdings, estimated at roughly 340,000 scanned images, has been circulated internally as a starting point.

Cost is the sticking point. Comparable deduplication projects in comparable mid-size European cities have run anywhere from CHF 180,000 to CHF 420,000 depending on the degree of human review required for ambiguous matches — images that are near-identical but not pixel-perfect, such as consecutive frames from the same survey flight. Zurich's IT budget for 2026 earmarked CHF 2.1 million for digital infrastructure modernisation across all departments, and competing claims from the school network upgrade in Schwamendingen and the new public Wi-Fi rollout along Langstrasse mean the archive project is fighting for a modest slice of a contested pot.

The Decisions That Cannot Wait

Three choices will define the outcome. First, the Informatik-Kommission must decide whether to commission a city-wide audit or restrict the first phase to the Stadtarchiv. A narrower scope is cheaper and faster but leaves the larger problem at Geomatik + Vermessung Zürich untouched, potentially creating reconciliation headaches later when the two datasets eventually need to merge under the planned unified Open Data Zurich portal, scheduled for a soft launch in early 2027.

Second, administrators need to settle on a retention policy for images flagged as duplicates. Deletion is not automatic: under cantonal archiving law, certain categories of public-interest imagery must be preserved even if they are redundant, meaning the process requires legal sign-off from the Stadtschreiber's office on Stadthausquai, not just a technical purge.

Third, the city must decide whether to bring this into the standard procurement cycle or treat it as an urgent infrastructure repair — a distinction that affects both the timeline and which suppliers can bid. Procurement through the standard Beschaffungswesen process takes a minimum of four months. An urgency designation could compress that to six weeks but requires sign-off at the Stadtratsstufe.

The practical upshot for residents is less dramatic than it sounds, but real. A cleaner image archive means faster search results on the public-facing Stadt Zürich Open Data portal, lower energy consumption at the Altstetten data centre, and a more legally defensible data holdings record as cantonal auditors become more active. The summer recess is short. Officials who defer the call until September will find themselves behind the 2027 portal deadline before the autumn leaves are off the Lindenhügel.