Generating An Indication of Where A Mobile Unit Can Move To

A method of generating an indication of where, within a geographical region, a mobile unit can move to from a specified origin in the geographical region using a network of navigable elements in the geographical region and in accordance with a total movement budget specified for the mobile unit, the method including: for each sub-region of a set of one or more sub-regions of the geographical region, associating one or more corresponding utilization amounts with said sub-region; identifying an initial navigable element that corresponds to the origin; performing a sequence of steps, wherein each step includes: using an identification function to try to identify an additional navigable element, wherein the additional navigable element is a neighbour of an already-identified navigable element and can be reached by the mobile unit from the origin in accordance with the total movement budget; and in response to the identification function identifying an additional navigable element of at least one sub-region, performing an update for at least one utilization amount corresponding to a sub-region for the identified additional navigable element; wherein, for each sub-region of the set of one or more sub-regions, the identification function is arranged to ignore at least one of the unidentified navigable elements of that sub-region if a group including the one or more utilization amounts that correspond to that sub-region and that have passed a corresponding predetermined threshold meets an ignore criterion; and generating the indication of where the mobile unit can move to according to the navigable elements that have been identified.