PROPERTY — BOUNDARY SURVEY
You opened Géoportail, overlaid the cadastral map on the satellite photo, and spotted that small gap. Ever since, you’ve been convinced: your neighbor built their fence 30 cm onto your land. But an on-screen overlay is no substitute for a proper topographic survey. On the Côte d’Azur, actual boundaries often shift by 50 cm to 1 m compared to the cadastral record, due to land remodeling and historical inaccuracies. It’s not uncommon to see a case in Nice where the owner was certain of a 40 cm encroachment… the boundary survey showed they were in fact on their own land, 20 cm short of the line.
What you see — and what it’s actually hiding
You line up the cadastral map with the satellite photo, measure it on screen with a ruler, and it looks obvious. But the cadastral map isn’t a surveying document: its accuracy is on the order of a meter in rural areas, sometimes 50 cm in town. The satellite photo has a resolution of 30 cm to 1 m, and the overlay accuracy depends on orthorectification. In short, you’re stacking two sources of imprecision.
What no one tells you: the cadastre is a tax document, not a legal one. The only evidence that holds up is a contradictory boundary survey (bornage). In Nice, with sloped land and retaining walls, the error can reach 1 meter. On complex terrain, as is common on the Côte d’Azur with its hillsides and retaining walls, discrepancies can reach 1 meter. Without a professional topographic survey using a total station or GNSS, you remain uncertain about the actual boundaries.
The numbers that change everything: overlay uncertainty
To know whether the gap is significant, you need to estimate the total error. The root mean square error (RMSE) combines the uncertainties: RMSE = √(σ_cad² + σ_photo²). In an urban area of Nice, the cadastral uncertainty σ_cad ≈ 0.5 m. A standard orthorectified satellite photo has σ_photo ≈ 0.3 m. That gives RMSE = √(0.5² + 0.3²) = √(0.25 + 0.09) = √0.34 ≈ 0.58 m. In practical terms, a 58 cm gap falls within the margin of error! Your 30 cm gap is therefore not statistically significant.
What this means in practice: as long as the gap is below 2× RMSE (i.e. 1.16 m), you cannot conclude there is an encroachment. A contradictory boundary survey with a licensed surveyor (géomètre-expert) brings the uncertainty down to ±2 cm. That’s the only way to settle the matter. Article 646 of the French Civil Code requires a boundary survey in the event of a dispute, and Decree 2011-1309 specifies that only a licensed surveyor can carry it out.
What happens if you do nothing
You leave things as they are. In 6 months, nothing will have changed. But in 2 years, if you sell, the buyer will require a boundary survey and will uncover the gap. You’ll then have to negotiate an easement or move the fence at your own expense. In Nice, an amicable boundary survey costs €1,500 to €2,500. In a contested case, expect €5,000 to €10,000 including lawyer and court-appointed expert fees.
Worse: if the encroachment is real and the neighbor builds a wall or a pool, thirty-year acquisitive prescription may come into play. In 30 years, you could permanently lose that strip of land. It’s not uncommon to see a case in western Nice where the owner waited 15 years: the fence had become the legal boundary through prescription.
Remedies and guarantees: what you can demand
You can demand a boundary survey under Article 646 of the Civil Code: « Any property owner may compel their neighbor to have their adjoining properties surveyed and marked. » The procedure: send a registered letter with acknowledgment of receipt to your neighbor, proposing an amicable boundary survey carried out by a licensed surveyor. If they refuse, take the matter to the Nice judicial court. The licensed surveyor draws up a boundary report (procès-verbal de bornage), which stands as valid proof unless disproved. Act quickly: the longer you wait, the more complicated the situation becomes.
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📅 Updated on 18/08/2026 — By Cassini Expertise, independent building expert serving Alpes-Maritimes (06) & Var (83). Free quote: 04 22 46 06 04.
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Frequently Asked Questions
How do I know if my neighbor is encroaching on my property?
Compare the cadastral map with your property’s actual boundaries. If structures or fences extend beyond the indicated limits, there is likely an encroachment. You can also call in a licensed surveyor for a precise boundary survey.
What should I do once an encroachment is confirmed?
Start by talking with your neighbor to reach an amicable agreement. If that fails, send a formal notice. As a last resort, take legal action to have the encroachment stopped and to claim damages.
What’s the difference between the cadastral map and a satellite photo?
The cadastral map is an official document showing the legal boundaries of parcels, but it can be imprecise. A satellite photo shows the actual state of the land, but has no legal value. For legal proof, only a boundary survey carried out by a licensed surveyor stands as valid.
Cassini Expertise
Expert du bâtiment indépendant — Antibes (06·83·13·40)
📅 Mis à jour le 25/09/2026 — Cassini Expertise, expert bâtiment indépendant (06·83·13·40).