LAND LAW — BOUNDARY SURVEY
You’ve received a letter from your insurer: your neighbor is claiming 2 m² of your garden. You open Géoportail, overlay the cadastral plan on the satellite photo, and there it is — a 30 cm strip that appears to be missing. 30 cm may not sound like much, but in Nice, buildable land runs close to €5,000 per square meter. So you measure with a ruler, run the numbers again: it doesn’t add up. You’re convinced you’re right. Yet legally, you have nothing.
What you’re seeing — and what it’s actually hiding
The cadastral plan is not a surveying document. It was designed for property tax purposes, not to establish property boundaries. Its accuracy? At best 1 meter in urban areas. Google Maps? Even worse: the imagery is rectified and geo-referenced with tolerances of 2 to 5 meters. You’re comparing two data sets that don’t share the same level of precision.
What I regularly find on site in Nice is that homeowners assume the cadastral line is sacred. In reality, the true boundary is set by survey markers — where they still exist. And if they’ve disappeared, it takes a chartered land surveyor to re-establish them through a contradictory boundary survey. It’s not unusual to see cases where an apparent 20 cm encroachment vanished after a precise topographic survey — and others where a 5 cm discrepancy was hiding a forgotten right of way.
The calculations that change everything: the real accuracy of the cadastre
To understand why your overlay proves nothing, you need to look at the root mean square error (RMSE). In surveying, the uncertainty of a cadastral survey is given by: RMSE = √(σ₁² + σ₂² + … + σₙ²). For Nice’s vector cadastral plan (PCI), the stated accuracy is around 1 meter in urban areas. But that 1 meter is an RMSE, not a maximum error. In practice, most points fall within 1 meter of reality, and 95% within 2 meters. So your 30 cm discrepancy sits comfortably within the cadastre’s margin of error. Legally, it proves nothing.
What nobody tells you: Decree 2011-1309 requires that boundaries be established by a chartered land surveyor using far tighter tolerances. For a court-ordered boundary survey, the tolerance is 5 cm in urban areas. Your homemade calculation measured the distance between your wall and the cadastral boundary shown on Géoportail. But the cadastral plan isn’t geo-referenced with the precision of RTK GNSS. As a result, your 30 cm gap could simply be down to image distortion. What does that look like in practice? This kind of case often reveals a 45 cm discrepancy between the cadastre and an RTK survey. In one case, the neighbor had already had a fence installed. The boundary survey showed the cadastre itself was 40 cm off. The homeowner won — but only after already paying €3,000 in legal fees.
What happens if you do nothing: acquisitive prescription
In Nice, inaction can cost you dearly. If your neighbor occupies that strip of land for 30 years, continuously, peacefully, and without dispute, they can become its legal owner through acquisitive prescription (Article 2258 of the French Civil Code). And 30 years passes faster than you’d think. In neighborhoods like Cimiez or Fabron, it’s not unusual to see 15-year-old encroachments turn into rights of way by implied grant. The problem is that as long as you don’t act, your neighbor can keep building, planting, fencing. And demolition later comes at a price: budget €200 to €400 per m² to demolish a foundation in Nice.
Another risk: if you sell your property, the buyer can demand a boundary survey beforehand. An encroachment discovered during the sale agreement can derail the deal entirely, or justify a 10 to 20% price cut. It’s not unusual to see an apartment in Nice lose €30,000 in value over an unresolved 50 cm encroachment. Frankly, you’re better off acting now.
Remedies and guarantees: what you’re entitled to demand
The legal basis is Article 646 of the French Civil Code: « Any property owner may compel their neighbor to establish the boundary between adjoining properties. » Decree 2011-1309 specifies that the boundary survey must be carried out by a chartered land surveyor, with the boundaries set on a contradictory basis. The process: send your neighbor a registered letter with acknowledgment of receipt requesting an amicable boundary survey. If they refuse, you can bring the matter before the Nice judicial court. In the meantime, don’t change anything — no fencing, no planting. A bailiff’s report with photographs can help build your case. But the real groundwork is the contradictory topographic survey. Using a Leica TS16 total station and RTK GNSS, I can pinpoint the true boundary to within ±2 cm. The chartered land surveyor then draws up the official boundary report, which becomes the legal reference. The cost? Budget €1,500 to €3,000 for a straightforward boundary survey in Nice — far less than a lawsuit.
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📅 Updated on 08/04/2026 — By Cassini Expertise, independent building expert covering the 06 & 83 départements. Free quote: 04 22 46 06 04.
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Frequently asked questions
What should I do if my neighbor has built on my land?
Act quickly. Consult a lawyer specializing in construction law to review your rights and the remedies available. Then send your neighbor a formal notice demanding demolition or compensation. If no agreement is reached, you can bring the matter before the judicial court.
Is the cadastral plan legally conclusive in an encroachment dispute?
No, the cadastral plan is a tax document, not a legal document proving ownership. It can serve as an indication, but only the title deed (notarized deed) and a boundary survey carried out by a chartered land surveyor are legally conclusive. In a dispute, a judge can order a court-mandated boundary survey.
Can I use Google Maps to prove an encroachment?
Google Maps can show how construction has evolved over time, but it has no legal evidentiary value. It can be used as contextual evidence, but you’ll need stronger proof, such as a land surveyor’s report, dated photographs, or witness statements. For court proceedings, you’ll need solid technical and legal evidence.
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).