Sardinia world (22 centenarians/100,000 inhabitants). Sardinia is the first discovered Blue Zone, a demographic and/or geographic area in the world with an oversize concentration of centenarians and supercentenarians. In 2016 there were 50,346 foreign national residents, forming 3% of the total Sardinian population. The most represented nationalities were: Sardinia's most populated cities are Cagliari and Sassari. The Metropolitan City of Cagliari has 431,302 inhabitants, or about ¼ of the population of the entire island. Eurostat has identified in Sardinia two Functional Urban Areas: Cagliari, with 477,000 inhabitants, and Sassari, with 222,000 inhabitants. Sardinia is one of the five Italian autonomous regions,
Sardinia mainland peninsula. The Strait of Bonifacio is directly north of Sardinia and separates Sardinia from the French island of Corsica. The coasts of Sardinia [ long] are generally high and rocky, with long, relatively straight stretches of coastline, many outstanding headlands, a few wide, deep bays, rias, many inlets and with various smaller islands off the coast. The island has an ancient geoformation and, unlike Sicily and mainland Italy, is not earthquake-prone. Its rocks date in fact from the Palaeozoic Era (up to 500 million years old). Due to long erosion processes, the island's highlands, formed of granite, schist, trachyte,