What Géorisques does not tell you about Paris
A Paris owner trying to find out whether a former quarry runs under their building hits a dead end: the national Géorisques portal does not publish underground cavity data for Paris. This page documents that gap, then releases as open data the only indicator that can be measured from the public data available: the share of each district covered by a risk sector of the local planning code.
The gap, in the words of the public service itself
BRGM, which operates Géorisques, states it explicitly: information on underground cavities and quarries is not available for Paris, and enquiries must go to the Inspection générale des carrières covering Paris and the inner suburbs (92, 93, 94). In practice requests are filed by notaries and surveyors during property transactions, through a paid online service.
On the Géorisques portal itself, cavity data is withheld for départements 75, 78, 91, 92, 93, 94 and 95. The direct and little-known consequence: the statutory risk statement handed over in a Paris sale says nothing about quarries or gypsum, even though these are the capital's two main underground hazards.
- BRGM — why cavity information is not available for Paris
- Géorisques — underground cavities, scope of the published data
- City of Paris — Inspection générale des carrières, everything about the underground
The barometer: 43.7% of Paris lies in a risk sector
In the absence of open cavity data, the City of Paris publishes the risk sectors appended to its bioclimatic local planning code: 23 polygons for quarries and 11 for gypsum. Cross-referencing them with district boundaries yields a measure that is comparable from one district to the next, and that nobody had published in this form until now.
| District | Area | Quarry sector | Gypsum sector | At least one of the two |
|---|---|---|---|---|
| 10th arrondissement Entrepôt | 289 ha | 45,7 % | 100,0 % | 100,0 % |
| 18th arrondissement Buttes-Montmartre | 600 ha | 34,8 % | 94,6 % | 100,0 % |
| 14th arrondissement Observatoire | 562 ha | 99,9 % | 0,0 % | 99,9 % |
| 19th arrondissement Buttes-Chaumont | 679 ha | 30,9 % | 80,9 % | 88,0 % |
| 13th arrondissement Gobelins | 715 ha | 85,7 % | 0,0 % | 85,7 % |
| 9th arrondissement Opéra | 218 ha | 14,6 % | 74,5 % | 74,5 % |
| 17th arrondissement Batignolles-Monceau | 567 ha | 1,9 % | 68,8 % | 68,8 % |
| 5th arrondissement Panthéon | 254 ha | 60,2 % | 0,0 % | 60,2 % |
| 6th arrondissement Luxembourg | 215 ha | 56,8 % | 0,0 % | 56,8 % |
| 2nd arrondissement Bourse | 99 ha | 0,0 % | 47,9 % | 47,9 % |
| 15th arrondissement Vaugirard | 850 ha | 43,3 % | 0,0 % | 43,3 % |
| 20th arrondissement Ménilmontant | 598 ha | 29,4 % | 1,1 % | 30,0 % |
| 3rd arrondissement Temple | 117 ha | 0,0 % | 19,4 % | 19,4 % |
| 16th arrondissement Passy | 1 637 ha | 15,0 % | 0,0 % | 15,0 % |
| 11th arrondissement Popincourt | 366 ha | 2,9 % | 10,4 % | 12,5 % |
| 7th arrondissement Palais-Bourbon | 409 ha | 8,5 % | 0,0 % | 8,5 % |
| 12th arrondissement Reuilly | 1 632 ha | 8,5 % | 0,0 % | 8,5 % |
| 8th arrondissement Élysée | 388 ha | 2,1 % | 6,3 % | 8,4 % |
| 1st arrondissement Louvre | 182 ha | 0,0 % | 0,0 % | 0,0 % |
| 4th arrondissement Hôtel-de-Ville | 160 ha | 0,0 % | 0,0 % | 0,0 % |
| Paris proper | 10 537 ha | 28,7 % | 19,9 % | 43,7 % |
- In total, 43.7% of the surface of Paris proper lies within a quarry or gypsum risk sector — roughly 4,604 hectares out of 10,537.
- The 10th district is the most affected, with 100.0% of its surface in a risk sector.
- Quarry risk peaks in the 14th district (99.9% of its surface), gypsum risk in the 10th (100.0%).
- Only 2 districts are entirely outside any risk sector: the 1st and the 4th.
- The two hazards overlap in north-eastern Paris, which is why the two columns sometimes add up to more than the last one.
Method
The polygons of both risk-sector datasets are reprojected to Lambert-93 (EPSG:2154), merged by theme to remove overlaps, then intersected with the administrative boundaries of the 20 districts. The share shown is the ratio of the intersected area to the district's total area. The calculation is reproducible: the script is published in the site's repository and all three datasets can be downloaded freely from Paris Data.
- Paris Data — bioclimatic planning code, quarry risk sectors
- Paris Data — bioclimatic planning code, gypsum risk sectors
- Paris Data — district boundaries
Three limitations worth keeping in mind
- A risk sector is not a quarry
- It is a regulatory perimeter that triggers planning obligations and a referral to the IGC. It also covers plots with no known cavity. A high percentage therefore does not mean that every other building sits above a void.
- The woods distort the surface comparison
- The 12th and 16th districts include the Bois de Vincennes and the Bois de Boulogne, which inflates their total area and mechanically lowers their percentage. The hectare figures in the downloadable file allow a different reading.
- Nothing replaces the IGC record
- Only the information record issued by the Inspection générale des carrières counts as official information at plot level. This barometer is a statistical benchmark, and this site's pre-assessment an informational guidance tool.
Reusing this data
The data is released for free reuse under the ODbL licence, like the source datasets.
Download the CSV Download the JSON
Original data: City of Paris — Paris Data, ODbL licence. Calculation and presentation: Sous-sol Paris. To cite this page: Sous-sol Paris, “Paris underground barometer”, 15 September 2026, https://www.sous-sol-paris.com/en/donnees/.
Calculated on 15 September 2026.