By Mark Doyle
BBC News, DR Congo
President Kabila is credited with bringing peace to the east
One important aspect of the Democratic Republic of Congo's post-war election campaign which reaches its conclusion on Sunday is that the country has been broadly split politically into language areas.
In the first round of voting, when there were over 30 candidates, there was a strong tendency for the incumbent President Joseph Kabila to do well in the east, where the lingua franca is Swahili.
His main rival in the run-off presidential contest, Jean-Pierre Bemba, did well in the west, where most people speak Lingala.
The United Nations mission has called on the two rivals to make public appeals for calm among their supporters but tensions remain high because the two belligerents during the war both still have loyal armed forces.
The voting division is partly an ethnic split, but not entirely.
Swahili is spoken across many countries in east and southern Africa and in DR Congo, it is spoken by many different tribes.
Jean-Pierre Bemba has more support in the capital, Kinshasa
Mr Kabila may have been popular in the east across tribal boundaries because this is the part of the country which suffered most in the war and he has successfully portrayed himself as the man who invited UN troops in to help end the conflict.
Mr Bemba, on the other hand, is popular in the capital, Kinshasa and in his nearby home state of Equator.
Both are places where the vast majority speak Lingala.
The areas around the capital are now the key battleground for votes.
Mr Kabila won more votes overall than Mr Bemba in the first round of the elections, but did badly in Kinshasa.
The first round results showed a geographical divide in support
So, one of Mr Bemba's tactics is to aim for a higher turnout of voters in the densely populated Lingala-speaking areas around Kinshasa.
Mr Kabila, on the other hand, will try to hang on to his Swahili-speaking vote and at the same time, try to reach out to Lingala-speaking politicians in the hope that they can deliver him vital swing voters.