The polka dot jersey or 'King of the Mountains' classification goes to the rider with the most points gained on categorised climbs throughout the Tour de France.
Each key climb within the race is ranked over 5 categories, from 1-4 (4 being the hardest) and the ultimate Hors Category, which is so tough it's un-categorised. Prior to the stage the riders are given the below information which categorises the climbs on each stage so they know where the points can be gained, and can work out how many are at stake at each point.
Mountain climbs were introduced in the Tour de France in 1910, when the route went over the Col d'aubisque and the Col de Tourmalet in the Pyrenees. At the time the routes through the mountains were barely tracks used by farmers and shepherds, and the riders slowly wound their way up the mountains with their heavy, non geared bikes. The Alps were introduced into the race the year after.
The King of the Mountains has been awarded in the Tour since 1933, and it became known as the Polka dot jersey, or Maillot a pois rouges, in 1975. The spots came from the sponsors at the time, a chocolate manufacturer called Chocolat Poulain. One of their products was packaged with the polka dots so it was deemed appropriate sponsorship to make the jersey spotty too. The sponsors have changed over the years but the polka dots have stayed and become part of the Tour's DNA.
The cyclist who has won the polka dot jersey the most is Richard Verenque, winning it 7 times. In more recent years the winners have been
2012 - Thomas Voeckler
2013 - Nairo Quintana
2014 - Rafal Majka
Currently the holder of the jersey is Chris Froome. At the start of today's stage he has 61 points, in second place is Joachim Rodriguez on 52pts. Tradition is if the Leader of the GC also has the polka dot jersey then the rider in second place will wear it for that days stage. So today Rodriguez will be wearing the spots!
Earlier in the Tour history was made when Daniel Teklehaimanot became the first African to don the polka-dot jersey. He is racing for the first ever African pro team to race in the Tour, Eritrea and MTN-Qhubeka. So double history was made when he took to the podium after stage 6.
With 4 more stages in the mountains the final winner of the Polka dot jersey is tricky to predict. It could certainly stay with Froome, but it wouldn't take much for his rivals such as Quintana or Contador to quickly clock up a lot of points as they take on some of the toughest climbs in this years race.