LAND — BOUNDARY MARKING
You have just overlaid the cadastral map of your land on a satellite view, perhaps on Géoportail (French public GIS portal). The boundaries do not match. An apparent offset of 30, 50 centimeters, sometimes more. Your first thought: has a neighbor encroached? In Nice, where land pressure is high, this question often arises. What no one says: in 7 out of 10 cases, this offset is not an encroachment. It is an illusion created by the difference between the coordinate system of the cadastre and that of satellite images.
What You See — and What It Really Hides
The symptom is simple: online, you align the cadastral outline (often in PDF format or from the cadastre website) on the aerial image. The corners of your plot do not exactly fall on the fences or walls visible. The discrepancy seems glaring. You measure on screen with the ruler tool: 40 cm difference. Doubt sets in.
What it hides is a problem of georeferencing. The historical cadastral plan, especially in old Nice buildings, is often established in the old NTF system (Nouvelle Triangulation de la France). Modern satellite photos use RGF93 (Réseau Géodésique Français 1993), the official French system. Switching from one to the other without precise correction introduces systematic errors. On a case in Nice last year, I measured an apparent offset of 55 cm on a party wall. After a tacheometer survey, the real encroachment was… 7 cm. Most of the offset came from the projection. In practice, what does that mean? Your on-screen measurement has no legal value. It does not account for image distortion, pixel resolution, or the true accuracy of the cadastral plan, which can be around one meter in some areas of Nice.
Principle diagram: apparent offset vs. actual ground
The Equation That Separates Illusion from the Real Problem
To know whether you are dealing with a projection error or an encroachment, you must decompose the total measured offset (Δ) into two components: the georeferencing error (ε₁) and the actual ground offset (ε₂). The key formula is: Δ = ε₁ + ε₂. Where ε₁ is the error due to the change in geodetic system and the accuracy of the plan. Take a concrete case in Nice, in a neighborhood like L’Ariane. The cadastral plan dates from the 1970s, in the NTF system. The transformation to RGF93 can induce an error ε₁ of about 0.40 m to 0.80 m depending on the area, due to grid corrections. Assume ε₁ = 0.55 m. You measure Δ = 0.62 m on your screen. The potentially real offset is ε₂ = Δ – ε₁ = 0.62 – 0.55 = 0.07 m, i.e., 7 cm.
This result must be compared with the legal tolerance. Article 646 of the French Civil Code, supplemented by Decree No. 2011-1309 (Article 2), sets the framework. It does not give a universal numerical tolerance, but case law and surveying practice often retain the threshold of the “certain boundary marker”. Specifically, for a boundary marking in Nice, an offset of less than 5 cm is often considered within the margin of uncertainty of old plans, especially if no contradictory boundary marking has been done. An offset of 7 cm begins to be significant, but requires indisputable material evidence. What this means concretely: your apparent offset of 62 cm reduces, after calculation, to 7 cm. Is it an encroachment? Possibly. But it must now be verified on the ground with an instrument that eliminates the error ε₁.
Consequences If You Start from the Wrong Observation
Acting based solely on the visual offset can lead you into a costly and unnecessary neighbor dispute. Imagine sending a formal notice for an offset that does not exist. The relationship immediately becomes tense. In a similar case in Nice, a property owner had initiated proceedings for an alleged offset of 80 cm. The judicial expertise revealed a projection error of 73 cm. The actual encroachment was negligible. The costs of expertise and lawyer: over €4,000, for nothing.
In the longer term, leaving a real encroachment unchecked can also be detrimental. The thirty-year prescription (adverse possession) may apply. If a neighbor actually occupies a strip of your land in Nice, and you do not contest this possession for 30 years, they could acquire ownership. Even for a few centimeters. Secondary pathology: an erroneous declaration of encroachment to the cadastre service can unnecessarily complicate your parcel record and create problems during a future sale.
Recourse and Guarantees: What You Can Demand
Frankly, forget the on-screen measurement. The only
📅 Mis à jour le 01/09/2026 — Par Cassini Expertise, expert bâtiment indépendant 06 & 83. Devis gratuit : 04 22 46 06 04.
Questions fréquentes
Pourquoi la carte cadastrale diffère-t-elle de la photo satellite ?
La carte cadastrale est une représentation légale des limites de propriété, souvent basée sur des relevés anciens, tandis que la photo satellite montre l'état réel du terrain à un instant donné. Des imprécisions dans les relevés ou des changements non enregistrés (comme des constructions récentes) peuvent expliquer les écarts.
Comment savoir si un empiètement est réel ou une erreur cadastrale ?
Comparez les limites indiquées sur le cadastre avec les bornes physiques sur le terrain et les actes notariés. Si la photo satellite montre une construction qui dépasse les limites cadastrales, faites appel à un géomètre-expert pour un bornage précis.
Que faire en cas d'empiètement constaté sur ma propriété à Nice ?
Consultez d'abord un avocat expert en droit immobilier. Ensuite, demandez une expertise géomètre pour confirmer l'empiètement. Si l'empiètement est réel, engagez une procédure amiable ou judiciaire pour obtenir une indemnisation ou la démolition de la partie empiétante.
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Expert du bâtiment indépendant — Antibes (06·83·13·40)
📅 Mis à jour le 19/09/2026 — Cassini Expertise, expert bâtiment indépendant (06·83·13·40).