1. A method of determining data indicative of an individual driver workload, the method comprising: obtaining generic driver workload data, the generic driver workload data being representative of a generic driver workload when performing a manoeuvre at a node or traversing a set of one or more segments of an electronic map; generating an individual modifier representative of the behaviour of an individual driver; and using the individual modifier to determine individual driver workload data indicative of the workload of the individual driver when performing the manoeuvre at the node or traversing the one or more segments of the electronic map based on the generic driver workload data for the manoeuvre at the node or the traversal of the one or more segments.