Democratizing French Real Estate Data: How RefCadastrale.fr simplifies BDNB and DVF open datasets for citizens

Hello Community Managers,

I would like to propose a Data Story highlighting a practical use case of French Open Data: RefCadastrale.fr (https://refcadastrale.fr).

The Challenge: The French government provides incredibly rich open datasets, such as the National Building Database (Base de Données Nationale des Bâtiments - BDNB), Cadastral Parcels (API Carto IGN), and Real Estate Transactions (Demandes de Valeurs Foncières - DVF). However, these datasets are often massive (e.g., the BDNB GeoPackage alone is over 150 GB) and difficult for the average citizen to navigate, cross-reference, and understand.

How Open Data is Used: The project, RefCadastrale.fr, aggregates, optimizes, and links these massive datasets to make them accessible to everyone through a fast and intuitive web interface. It uses a data pipeline that:

1. Extracts and partitions the massive BDNB dataset into lightweight data shards per municipality.
2. Cross-references this with the DVF dataset to provide historical real estate transaction values.
3. Integrates data from the SITADEL dataset (construction permits) and the IGN API Carto for parcel geometries.

The Impact: Instead of requiring users to download gigabytes of raw data or use complex GIS software, any citizen can now simply search for an address or browse a map to instantly see a property's cadastral boundaries, energy performance (DPE), environmental risks, and past transaction values.

The developers have also open-sourced some of their extraction tools (like the Cadastre API Extractor) to help other developers work with the IGN API more easily.

I believe this would make a great Data Story to illustrate the end-user value of cross-referencing multiple national open datasets.

Best regards,