Lagos - Nigerians vote on February 16 to choose a president to lead Africa's biggest oil producer and, by some measures, the continent's largest economy.
The story behind the election in Africa's biggest democracy can be told in numbers.
* The size of Nigeria's population is hotly debated. The present figure of about 190 million is based on projections from a 2006 census that some experts say was flawed. Nevertheless, Africa's most populous country has 84 million people registered to vote in this weekend's election, a 25 percent rise from the last such vote four years ago, according to the national electoral commission.
* But turnout was just 44 percent in 2015. That puts Nigeria 41st out of 44 African countries, measured by the International Institute for Democracy and Electoral Assistance on their last presidential election turnout.
* Elections show how men dominate politics in Nigeria. Although 47 percent of registered voters are women, according to the electoral commission, their political representation is limited. The country has never elected a woman president or state governor, and women only make up 6 percent of the 469 national parliament members. For national and gubernatorial elections, women make up roughly one-in-eight of the 8 878 total candidates, while for the presidency alone they are 7 percent of the 71 candidates.
* Almost a quarter of registered voters - 24 percent - live in Buhari's heartland in the northwest, according to the electoral commission. The next-largest region by vote is the southwest, home to Lagos, the metropolis where Buhari's political godfather Bola Tinubu helped deliver victory in 2015. Opposition figures have been campaigning in these areas to try to unseat the incumbent.
* Nigeria's population is young and fast-growing – it is expected to be the world's third most populous country by 2050 with 400 million inhabitants, the United Nations says. More than half of all voters, 51.1 percent, are between 18 and 35, according to the electoral commission. The country's median age is 18 years old. The two main presidential contenders are in their 70s - Buhari is 76 and the main opposition candidate, Atiku Abubakar, is 72.
* Nigerian elections can be deadly: more than 800 people were killed in 2011 in post-election protests in the north after Buhari's defeat that year, according to Human Rights Watch. In 2015, more than 160 people were killed in election-related violence, the European Union has said. Observers have called for violence-free elections this time but concerns remain high, especially if the losing candidate refuses to concede. Several people were killed in a stampede at a Buhari rally in Port Harcourt.
* Three hundred metres: a variety of activities related to campaigning are forbidden within this distance of a polling unit, according to the 2010 electoral act, including a ban on offensive weapons affecting even police. Moreover, a court ruled in 2015 that the military must not be involved in elections. However, the electoral commission said armed police and soldiers would guard polling units where the 1.8 million people who have fled Islamist violence in the northeast will vote.
* This will be Nigeria's sixth election since returning to democracy in 1999, after decades under the military.