KEY POINTS:
In the old days, an electoral map of France would show the country divided up into recognisable political tribes like the parts of a cow in a butcher's shop diagram.
In the northern and eastern coal-mining and steelmaking belts, voters would be dependably Socialist or Communist. In the Catholic stronghold of Brittany, sentiment was invariably Gaullist.
Voters in the heart of Paris would be conservative but the city's outskirts were always a red belt of backing for the left. In the south, the far-right could count on votes among pensioners and poor whites worried about immigration.
Today, though, some of these reassuring regional traditions have been shaken up and others may have been swept away for good, as rapid economic change and disaffection with mainstream politics remould France's social structure and its voting patterns.
Many electors who loyally stood by a party through thick and thin now admit they are undecided or may register a protest vote.
These swing voters hold the keys to the Elysee presidential palace, and the candidates bidding to become head of state are tirelessly working the regions, sculpting their message according to need, ahead of Sunday's first round of balloting.
In the 2002 presidential elections, voters in the blue-collar former coal-mining area of Nord/Pas-de-Calais in northern France had been expected to stick with tradition and cast their ballots for the Socialist candidate.
Instead, the far-right's Jean-Marie Le Pen came in first with more than 19 per cent of votes. The Socialists' Lionel Jospin came in third, behind Jacques Chirac.
"Up until 2002, I always voted for the left," said Elie Trinez, a resident of the border town of Tourmignies.
"I've moved to the right, like many people here."
The move towards the nationalists dumbfounded local analysts, given that the region benefits more than any other from European Union regional aid and has benefited hugely from cross-border trade with Britain, through the Channel Tunnel, and neighbouring Belgium.
The underlying reason: unemployment. Joblessness in the north affects one in eight of the workforce, the second highest in France, and one in four among the young.
Farther south in France's heartland, Burgundy, the big issue is Europe. The region is famous for its wines, and locals want a President who will have clout in Brussels to ensure that the subsidy tap is kept open in a time of globalisation.
In Brittany, regional autonomy, farming and religion figure high on the agenda, and centrist Francois Bayrou, a gentleman farmer, is well-placed, according to a commentary by the region's Brittany Press Agency.
In the tense, high-immigration housing estates around the southern city Marseille, one of the surprises has been the success of Jose Bove, the champion of small farmers and darling of anti-globalisation protesters.
In Sunday's poll, if no candidate garners an outright majority, the first two in the field go to a runoff vote two weeks later. The frontrunner is the conservative Nicolas Sarkozy, followed by the Socialists' Segolene Royal and then Bayrou and Le Pen.
All four are bunched together within a 10-percentage-point margin, making the election one of the closest in French history, according to opinion polls.
