# Neighbour Built on Your Land? Cadastral Map Not Enough > Voisin empiétant sur votre terrain à Nice : cadastre et Google Maps insuffisants. Un lever précis s'impose pour sécuriser vos limites. - URL : https://cassini-expertise.fr/en/neighbor-built-on-your-land-cadastral-map-google-maps-not-enough-nice/ - Langue : en-US - Mis à jour : 2026-11-06 - Site : Cassini Expertise (https://cassini-expertise.fr/) PROPERTY – BOUNDARY MARKING You received a letter from your insurer: your neighbour claims 2 m² of your garden. You open Géoportail (French geoportal), overlay the cadastral map on the satellite photo, and there, shock: a 30 cm strip seems extra. 30 cm is not much, but in [Nice](https://cassini-expertise.fr/nice-secheresse-argile-fissures-donnees-officielles/), the price per square metre of buildable land is nearly €5,000. So you measure with a ruler, recalculate: it doesn’t match. You are sure you are right. Yet, legally, you have nothing. ## What You See – and What It Really Hides ![neighbor built on your land cadastral map google maps not enough nice - Cassini Expertise](https://cassini-expertise.fr/wp-content/uploads/2026/09/avant-achat-maison.webp) *Cassini Expertise – independent building expertise* The cadastral map is not a survey document. It was designed for property tax, not to delimit properties. Its accuracy? At best 1 metre in urban areas. Google Maps? Even worse: images are rectified, georeferenced with tolerances of 2 to 5 metres. You are comparing data that do not have the same precision. What I often see on site in Nice is that owners believe the cadastral line is sacred. However, the real boundary is the boundary markers, when they exist. And if they have disappeared, a *expert en urbanisme* (licensed surveyor) must re-establish them jointly. Frankly, I have seen cases where an apparent encroachment of 20 cm disappeared after a precise topographic survey. And others where a 5 cm difference hid a forgotten easement of way. ## The Calculations That Change Everything: Real Accuracy of the Cadastre To understand why your overlay is worthless, we need to talk about the root mean square error (RMSE). In surveying, the uncertainty of a cadastral survey is given by: RMSE = √(σ₁² + σ₂² + … + σₙ²). For the vector cadastral plan (PCI) of Nice, the stated accuracy is about 1 metre in urban areas. But note, this 1 metre is an RMSE, not a maximum error. Concretely, 68% of points are within 1 metre of reality, and 95% within 2 metres. So your 30 cm discrepancy is perfectly within the cadastre’s tolerance. Legally, it proves nothing. What no one says: boundary determination is reserved to chartered land surveyors (géomètres-experts), whose survey documents follow much finer precision classes (order of 16 September 2003 on survey documents). For a judicial boundary marking, centimetre-level precision is the norm. Your homemade calculation: you measured the distance between your wall and the cadastral boundary displayed on Géoportail. But the cadastral plan is not georeferenced with the precision of GNSS RTK. Result: your 30 cm discrepancy may be due to simple image distortion. In practice, what does that mean? On a case in Nice last year, I measured a 45 cm discrepancy between the cadastre and an RTK survey. The neighbour had already installed a fence. Result: the boundary survey showed that the cadastre had a 40 cm offset. The owner won, but he had already paid €3,000 in legal fees. ## What Happens If You Do Nothing: Adverse Possession In Nice, inaction can cost you dearly. If your neighbour occupies that strip of land for 30 years continuously, peacefully, and unequivocally, he may become owner by adverse possession (Article 2258 of the French Civil Code). And 30 years goes by quickly. In neighbourhoods like Cimiez or Fabron, I have seen encroachments 20 years old become easements by destination of the family head. The problem is that as long as you do not react, the neighbour can build, plant, fence. And then, demolition is expensive: expect €200 to €400 per m² for foundation demolition in Nice. Another risk: if you sell your property, the buyer may require a prior boundary survey. The encroachment discovered during the preliminary sale agreement can cause the sale to fall through or justify a price reduction of 10 to 20%. I saw an apartment in Nice that lost €30,000 in value due to an unresolved 50 cm encroachment. So, frankly, better to act now. ## Recourse and Guarantees: What You Can Demand The legal basis is Article 646 of the Civil Code: “Any owner may compel his neighbor to the boundary marking of their contiguous properties.” French law reserves boundary marking to chartered land surveyors, and boundaries are set jointly (art. 646-647 of the Civil Code). The procedure: send a registered letter with acknowledgment of receipt to your neighbour requesting a boundary survey. If they refuse, you can take the matter to court (the *tribunal judiciaire*). The judge will order a judicial boundary survey, and the costs are typically shared. In urgent cases, you can request a summary proceeding (*référé*) to stop ongoing construction. Also, check your property insurance: some policies cover legal costs for boundary disputes. Finally, if the encroachment is recent (less than 30 years), you can demand removal of the construction at the neighbour’s expense, based on Article 545 of the Civil Code: “No one may be compelled to give up his property, except for public utility and with prior compensation.” ## Frequently asked questions ### What should I do if my neighbour has built on my land? In France, if your neighbour has built on your plot without permission, you need to act quickly. Consult a lawyer who specialises in property law to bring a claim for recovery of the land or for demolition. The limitation period is generally 30 years, but an action to stop the encroachment may be more urgent. ### Is the cadastral map authoritative in a boundary dispute? No, the cadastral plan is a tax document and is indicative only; it is not conclusive evidence of the real property boundaries. In a dispute, only a boundary survey carried out by a chartered land surveyor (géomètre-expert), who marks the boundaries according to the title deeds and evidence on the ground, has legal value. ### Can I use Google Maps as evidence of an encroachment? Google Maps can provide visual clues, but it has no legal evidential value because of possible distortion and inaccuracy. For solid evidence, you need to instruct a chartered land surveyor (géomètre-expert), who will produce an accurate survey and a boundary report (procès-verbal de bornage). **See also:** [Independent Building Expert – French Riviera](https://cassini-expertise.fr/en/) · [IGN Orthophoto vs Cadastral Map in Nice: Planimetric Error](https://cassini-expertise.fr/en/ign-orthophoto-cadastral-map-planimetric-error-nice/) · [Pool on the Property Line in Antibes: Boundary Recourse](https://cassini-expertise.fr/en/pool-property-line-antibes-boundary-recourse-art-674/) --- Source : https://cassini-expertise.fr/en/neighbor-built-on-your-land-cadastral-map-google-maps-not-enough-nice/