How Paris's Building Archives Ended Up Full of Duplicates — and What the City Is Finally Doing About It

Paris's Direction de l'Urbanisme holds tens of thousands of scanned building permits, cadastral maps and heritage photographs — and for years, nobody agreed on how many actually existed. The answer, it turns out, is complicated by the fact that a significant share of the archive's digital images appear more than once, sometimes four or five times over, filed under different reference numbers across incompatible databases.

The problem is not abstract. As the city moves to open its urban-planning records to developers, architects and neighbourhood associations pressing for transparency on projects tied to the Grand Paris Express and the post-Olympic Seine regeneration corridor, duplicate image files have slowed access, inflated storage costs and, in at least a handful of documented cases, caused different parties in planning disputes to work from different versions of the same document.

How the Duplication Built Up Over Twenty Years

The root of the mess stretches back to the early 2000s. Between roughly 2001 and 2018, Paris digitised its planning archive in at least four separate waves, each driven by a different budget cycle and handled by different contractors. The first major push, linked to a European Commission-funded urban-data initiative, used TIFF file formats and one naming convention. A second tranche, completed around 2009 by a consortium that included the Institut national de l'information géographique et forestière — better known as IGN — used JPEG compression and a different metadata schema. When the files were eventually migrated into a single municipal content-management system, the import scripts had no deduplication logic. Identical images arrived with different filenames and sat alongside their copies undisturbed.

By the time the Paris 2024 Olympics preparations accelerated demands on municipal data infrastructure — particularly around the Seine-Saint-Denis corridor and venues like the Stade de France in Saint-Denis — city technicians working with the Agence Parisienne du Climat and planning departments flagged the duplication issue formally in internal reviews. A 2023 audit of the Direction de l'Urbanisme's digital holdings, whose existence has been reported by Paris planning professionals, found that a material share of stored image files were redundant, though the city has not published precise figures from that document.

The Marais conservation zone illustrates the practical headache. Heritage officers at the Hôtel de Ville working on classified building files along Rue de Bretagne and around the Place des Vosges have reportedly had to manually cross-reference scans before using them, because the system cannot reliably flag which version of a document is the authorised original. That kind of manual verification step, multiplied across thousands of applications processed each year, absorbs significant staff time.

The Clean-Up and What Comes Next

The city launched a formal duplicate-image replacement programme in early 2025, contracted through the Direction des Systèmes et Technologies de l'Information. The technical approach uses perceptual hashing — a method that compares images based on visual content rather than file metadata — to identify near-identical scans even when compression or slight resolution differences make them technically distinct files. A pilot ran through the 10th and 11th arrondissement permit archives first, chosen partly because those districts have some of the densest application volumes in the city.

Full rollout is expected to reach the pre-1948 heritage photograph collections held at the Bibliothèque historique de la Ville de Paris on Rue de Rivoli by the end of 2026. Officials have also signalled that a cleaned archive will feed into the open-data portal at opendata.paris.fr, where urban planning datasets are increasingly sought by researchers, journalists and residents' associations lobbying on housing and rental-market questions.

For Parisians tracking development proposals — whether along the future Grand Paris Express Line 15 corridor or in the banlieue municipalities like Bobigny and Montreuil where housing pressure is acute — a reliable, deduplicated public archive matters more than it might sound. Clean records mean fewer procedural delays, fewer disputes over which plan version is operative, and eventually a faster pipeline from permit application to decision. The city has set no public deadline for declaring the full archive clean, but the work is, at last, under way.