Abstract: Disclosed herein is a method of determining an optimal route for a vessel based on vessel traffic data. The method comprises receiving vessel traffic data relating to the movement of each of a plurality of vessels in a geographical region and defining sub-regions within the geographical region in which the vessel traffic data has similar characteristics. The method also comprises determining an optimal route for a vessel between two geographical points using a representation of the geographical region. The representation comprises nodes, and each node is associated with a respective defined sub-region.