Nigeria is holding a crucial election which experts say is too close to call. Here's a look at Africa's most populous country and its biggest economy.

GEOGRAPHY: Nigeria is twice the size of California, with an area of nearly 360,000 square miles (579,000 square kilometers). It is set on the Gulf of Guinea on West Africa's Atlantic coast and borders Benin, Cameroon, Chad and Niger. Its topography ranges from mangrove swamps in the southern Niger Delta to semi-arid desert in the north.

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PEOPLE: Nigeria is home to an estimated 170 million people. Of more than 250 ethnic groups, the population is split between a predominantly Christian south and Muslim north. A small percentage practices indigenous beliefs. Twelve northern states have implemented Shariah law, an Islamic code of conduct, though the governments remain secular.

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LANGUAGE: English is Nigeria's official language; more than 500 local languages and dialects are widely spoken. The main three language groups are Yoruba, Hausa and Ibo.

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ECONOMY: Crude oil drives Africa's biggest economy, funding an estimated 80 percent of all government spending. Statistics suggest that 70 percent of Nigerians live in poverty on $2 or less a day. Despite endemic corruption, Nigeria is Africa's top destination for direct foreign investment and is a leading frontier market.

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THE ELECTION: President Goodluck Jonathan, a Christian who came to power after the death of the country's elected Muslim leader in May 2010, is in a close contest against former military ruler Muhammadu Buhari, who is backed by a coalition of opposition parties. If no clear winner emerges in the presidential poll, a runoff will be held.

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HISTORY: Nigeria gained independence from Britain in 1960. In 1967, the oil-rich eastern region tried to gain independence in a 30-month civil war that left more than 1 million dead. Peace and an oil boom in the 1970s brought in billions of dollars, but corruption has undermined prosperity and development. After decades of coups and military rule, Nigeria became a democracy in 1999.