A computer-implemented method for incrementally updating a geographic database comprising optimal routing information for a first geographic region and an adjacent second geographic region so that an optimal route between the first and second geographic regions can be found after updating optimal routing data for only the first geographic region, the method comprising: updating optimal routing information associated with the first geographic region, said updated optimal routing information comprising at least (i) new optimal routing information about one or more links in the first geographic region usable for optimally connecting to one or more links in the second geographic region, the new optimal routing information being based on updated link information for the first geographic region and (ii) previous optimal routing information about one or more links in the first geographic region usable for optimally connecting to one or more links in the second geographic region, the previous optimal routing information being based on un-updated link information for the first geographic region, wherein updating includes: computing a rank for each link of the first geographic region usable for connecting to one or more links of the second geographic region; determining for said each link whether the computed rank has a lower importance than a previous computed rank for said link; if so, retaining the previous computed higher importance rank as the rank for said link; and if not, making the newly computed rank the rank for said link, characterised in that the new optimal routing information is about one or more new links that were not present in the un-updated link information for the first geographic region and which represent one or more new roads which span the first geographic region and the second geographic region. updating optimal routing information associated with the first geographic region, said updated optimal routing information comprising at least (i) new optimal routing information about one or more links in the first geographic region usable for optimally connecting to one or more links in the second geographic region, the new optimal routing information being based on updated link information for the first geographic region and (ii) previous optimal routing information about one or more links in the first geographic region usable for optimally connecting to one or more links in the second geographic region, the previous optimal routing information being based on un-updated link information for the first geographic region, wherein updating includes: computing a rank for each link of the first geographic region usable for connecting to one or more links of the second geographic region; determining for said each link whether the computed rank has a lower importance than a previous computed rank for said link; if so, retaining the previous computed higher importance rank as the rank for said link; and if not, making the newly computed rank the rank for said link, computing a rank for each link of the first geographic region usable for connecting to one or more links of the second geographic region; determining for said each link whether the computed rank has a lower importance than a previous computed rank for said link; if so, retaining the previous computed higher importance rank as the rank for said link; and if not, making the newly computed rank the rank for said link, characterised in that the new optimal routing information is about one or more new links that were not present in the un-updated link information for the first geographic region and which represent one or more new roads which span the first geographic region and the second geographic region.