French Cerdagne

42°30′N 1°58′E / 42.500°N 1.967°E / 42.500; 1.967 French Cerdagne (Catalan: Alta Cerdanya, IPA: [ˈaltə səɾˈðaɲə]) is the northern half of Cerdanya, which came under French control as a result of the Treaty of the Pyrenees in 1659, while the southern half remained in Spain (as a part of Catalonia). Catalans often refer to French Cerdagne as Upper Cerdanya (Catalan: Alta Cerdanya). It is the only French territory on the Iberian Peninsula, as it is located on the south side of the Pyrenees Range between France and Spain.^[1][2][3] For example, the Segre river, which goes west and then south to meet the Ebro, has its source in the French Cerdagne. An inadvertent result of the Treaty of the Pyrenees is the Spanish exclave of Llívia (the small uncolored area in the map) which is sovereign Spanish territory surrounded by French Cerdagne.

French Cerdagne has no special status inside France, simply forming a physiographic region within the department of Pyrénées-Orientales, unlike the Spanish part of Cerdanya, which is officially a Catalan comarca called simply Cerdanya. In France, the French area is referred to as either Cerdagne française (i.e. "French Cerdagne"), Haute-Cerdagne (i.e. "Upper Cerdagne") or just Cerdagne.

French Cerdagne has a land area of 539.67 km² (208.37 sq. miles). Its 1999 population was 12,035, resulting in a density of only 22 people per km² (58 per sq. mile). The area has the most cloud-free days in France, ^{[citation needed]} and was therefore chosen as the place to build:

• the Odeillo solar furnace (official site), used for high-temperature scientific experiments;
• the Thémis experimental solar power plant (operated by EDF from 1983 to 1986); it is now decommissioned as a power plant, but is being used as a Cherenkov telescope for the detection of Gamma rays.^[4]