The Discworld Compass does not have North, South, East and West, like our own world's. Instead, the four directions are Hubwards (towards the Hub), Rimwards (towards the Rim), Turnwise (the direction that the Disc rotates in), and Widdershins (opposite to Turnwise).
Based on the fact that a needle of Octiron will always point towards the Hub, Hubwise could be said to be the Discworld's 'North', which would mean that Rimwards corresponds to South. The Disc turns clockwise, so Turnwise is on the left when you face the Hub; this would make Turnwise the Disc's West, and Widdershins would correspond to the East.