Cape Verde /ˌkeɪp ˈvɜrd/ or Cabo Verde /kɑːboʊ ˈvɜrdeɪ/ (Portuguese: Cabo Verde, pronounced: [ˈkabu ˈveɾdɨ]), officially the Republic of Cabo Verde, is an island country spanning an archipelago of 10 volcanic islands in the central Atlantic Ocean. Located 570 kilometres (350 miles) off the coast of Western Africa, the islands cover a combined area of slightly over 4,000 square kilometres (1,500 sq mi). Portuguese explorers discovered and colonized the uninhabited islands in the 15th century, the first European settlement in the tropics. Ideally located for the Atlantic slave trade, the islands grew prosperous and often attracted privateers and pirates, among them Sir Francis Drake in the 1580s. The islands were also visited by Charles Darwin's expedition in 1832. The islands were settled as the colony grew in importance on the main shipping lanes from Europe to India and Australia, and population increased steadily. At the time of independence from Portugal in 1975, Cape Verdeans emigrated across the world, such that the population in the 21st century of over half a million people on the islands is equaled by the diaspora in Europe, the Americas, and on the African continent. The Cape Verdean economy is mostly service-oriented with a growing focus on tourism and foreign investment, which benefits from the islands' warm year-round climate, diverse landscape and cultural wealth, especially in music. Historically, the name "Cape Verde" has been used in English for the archipelago and, since independence in 1975, for the country. In 2013, the Cape Verdean government determined that the Portuguese designation "Cabo Verde" would henceforth be used for official purposes, such as at the United Nations, even in English contexts.