1. A computer implemented method of performing a one-to-many route search on digital map data, said digital map data comprising a plurality of links connected by nodes representing navigable paths of a network, the method comprising: searching the map data using a one-to-many route planning algorithm to explore links from a departure node so as to determine a reachable area for the departure node, said searching comprising: determining a first cost for each explored link using a cost function associated with the route planning algorithm; and determining a second cost for each explored link using an objective function, such that each node reached by the route planning algorithm has a first accumulated cost and a second accumulated cost, wherein the first accumulated cost is the minimum accumulation of first costs for links forming a route from the departure node to the node, wherein the second accumulated cost is the accumulation of second costs for the links forming the route from the departure node to the node, and wherein the reachable area is based on a predetermined second accumulated cost value, such that a node is identified as unreachable when the second accumulated cost for the node exceeds the predetermined second accumulated cost value, wherein the searching of the map data is limited to a search boundary, wherein the first accumulated cost value defining the search boundary is based upon the first accumulated cost of the first unreachable node identified by the searching of the map data, the method further comprising: causing a representation of the determined reachable area to be displayed on a display device.