Copenhagen Leads Nordic Cities in Purging Duplicate Street Images From Public Records

Copenhagen's municipal technology office has been quietly working through a backlog of tens of thousands of duplicate street-level images embedded in the city's open urban data systems — a problem that has ballooned across European capitals as decades of overlapping mapping surveys, heritage documentation projects, and smart-city camera programs deposited redundant files into shared repositories with little coordination.

The issue matters now because cities are aggressively expanding their use of visual data to manage everything from pothole repair queues to flood-risk modelling. When the underlying image libraries contain duplicates — sometimes three or four near-identical frames of the same stretch of Nørrebrogade or the same façade on Bredgade — automated systems trained on that data can produce skewed outputs, inflating estimates of infrastructure wear or misidentifying change over time. The problem is not cosmetic. It directly affects how resources get allocated.

What Copenhagen Is Actually Doing

The effort sits inside Teknik- og Miljøforvaltningen, the city's technical and environmental administration, which oversees urban data standards across Copenhagen's 99 square kilometres. The administration has been running a deduplication programme since early 2025, using hash-matching algorithms to flag visually identical or near-identical image files across its GIS and street-survey databases. The programme targets imagery collected under the city's Byens Rum initiative, which catalogues public space conditions across neighbourhoods from Amager Vest to Vanløse.

The scale is considerable. Copenhagen's open data portal currently holds visual records linked to more than 140,000 individual address points, accumulated over surveys stretching back to 2009. City technicians working on the deduplication project have estimated, in internal documentation reviewed by The Daily Copenhagen, that roughly 18 to 22 percent of files in certain sub-categories were redundant before the programme began — a proportion that tracks closely with figures reported by Stockholm's Stadsbyggnadskontoret when it ran a comparable exercise in 2023.

Amsterdam's digital infrastructure team faced a similar reckoning in 2024. The Dutch capital's Gemeentelijke Basisadministratie project had accumulated duplicate imagery from at least four separate mapping contracts running concurrently across the canal ring district. Amsterdam ultimately contracted a third-party firm to perform the clean-up, a route Copenhagen has so far avoided, preferring to build the deduplication logic into its own systems at a reported internal cost lower than external procurement quotes.

How Copenhagen Compares Globally

Seoul is the city most often cited as the benchmark. The South Korean capital began systematic visual-data deduplication as early as 2021 under its Smart City Data Hub programme, integrating automatic duplicate detection directly into the image-ingestion pipeline so new uploads are checked before they enter the live database. Copenhagen has not yet reached that stage — its current programme is retrospective, not preventive — but Teknik- og Miljøforvaltningen has publicly indicated it intends to move toward real-time detection by 2027.

London's experience offers a cautionary note. The Greater London Authority's open data programme contains street imagery from at least six separate collection exercises conducted between 2015 and 2024, and the authority has acknowledged the duplication problem in published data quality reports without yet completing a systematic fix. Berlin is in a similar position: the Senatsverwaltung für Stadtentwicklung manages multiple overlapping imagery layers across the city's twelve boroughs, and deduplication work remains fragmented across district-level IT departments rather than handled centrally.

Copenhagen's centralised administrative structure — all urban data flowing through a single municipal authority rather than fragmented borough systems — gives it a structural advantage those cities lack. That said, the current programme covers only city-owned data. Commercial mapping imagery embedded in third-party applications used by Copenhagen planners falls outside its remit entirely, a gap technicians have flagged as a longer-term challenge.

For residents and businesses, the immediate practical effect is modest but real. Property developers submitting planning applications in areas like Ørestad and Sydhavn, where new construction surveys overlap with older baseline imagery, should expect faster processing as the city's systems become better at distinguishing current conditions from outdated records. The technical administration has indicated it expects to complete the retrospective clean-up phase before the end of 2026, at which point attention will shift to building the preventive infrastructure that Seoul and, more recently, Singapore have already put in place.