Short answer. The court uses the actual area you have been possessing, not the area stated in your title. Article 1135 of the Civil Code provides that when an adverse claimant possesses by mistake an area greater or less than what their title expresses, prescription is based on the possession, not the title.
What the law says
In case the adverse claimant possesses by mistake an area greater, or less than that expressed in his title, prescription shall be based on the possession.
Civil Code, Article 1135 — Possessing More Land Than the Title Shows. Read the full provision →
The rule: possession controls, not the title
Article 1135 of the Civil Code resolves a practical problem that often arises in land disputes: In case the adverse claimant possesses by mistake an area greater, or less than that expressed in his title, prescription shall be based on the possession. If you have been physically occupying and using a strip of land that your title does not cover, and you did so by mistake rather than deliberately, prescription runs on the area you actually possessed. The written title does not limit or expand the area that can be acquired through prescription — the actual facts of possession control.
Why the law looks at possession rather than paper
Acquisitive prescription rewards continuous, open, and peaceful possession over a period of time. The policy behind prescription is that the person who has been acting as owner — occupying, cultivating, enclosing, or improving the land — should eventually acquire legal recognition of what they have been treating as their own. It would be inconsistent with that policy to limit the area protected by prescription to what a title document says, when the actual possession on the ground may cover more or less. Article 1135 aligns the law with reality: the area of prescription is measured by what the possessor actually occupied, not by what paper documents describe.
Possessing more or less than the title states
The article covers both directions: possessing more than the title and possessing less. If your title describes a larger area but you have only been occupying a smaller portion, prescription may ripen only over the portion you actually possessed — the rest remains outside your prescription claim. Conversely, if you have been occupying a larger area than your title covers, prescription can ripen over the entire area you actually possessed, including the excess. In both cases, the critical question is what area was factually, continuously, and openly possessed throughout the prescription period.
The mistake requirement
Article 1135 applies specifically where the discrepancy between possession and title was a matter of mistake. This typically means the possessor did not deliberately set out to encroach on extra land but occupied it believing it fell within their proper boundaries. Where the possession of the excess was knowing and deliberate rather than mistaken, the analysis may differ. In practice, many boundary disputes involve exactly this kind of honest mistake — overgrown markers, imprecise surveys, or unclear monuments leading a possessor to occupy slightly more or less than their paper title says. Article 1135 addresses that common situation by anchoring prescription to the ground truth of actual occupation.